vs/EPA
National Lakes Assessment
J£ A Collaborative Survey of the Nation's Lakes
DRAFT
-------
U.S. Environmental Protection Agency (USEPA). 2009.
National Lakes Assessment: A Collaborative Survey
of the Nation's Lakes. EPA 841-R-09-001. U.S.
Environmental Protection Agency, Office of Water and
Office of Research and Development, Washington, D.C.
This report was prepared by the U.S. Environmental Protection Agency (EPA), Office of Water
and Office of Research and Development. It has been subjected to the Agency's peer review
and administrative review processes. This document contains information relating to water
quality assessment. It does not substitute for the Clean Water Act or EPA regulations, nor is it a
regulation itself. Thus, it cannot impose legally binding requirements on EPA, States, authorized
Tribes or the regulated community, and it may not apply to a particular situation or circumstance.
Cover photo courtesy of ©Ted C. McRae http://beetlesinthebush.wordDress.com
-------
Acknowledgements
The EPA Office of Water (OW) and the Office of Research and Development (ORD) would like to
thank the many people who contributed to this project. Without the collaborative efforts and
support by state environmental agencies, federal agencies, universities and other organizations,
this groundbreaking assessment of lakes would not have been possible. In addition, the survey
could not have been done without the dedicated help and support of enumerable field biologists,
taxonomists, statisticians and data analysts, as well as program administrators, regional
coordinators, project managers, quality control officers, and reviewers. To the many participants,
EPA expresses its gratitude.
Collaborators
Alabama Department of Environmental
Management
Arizona Department of Environmental Quality
Blackfeet Tribe, Environmental Program
California Department of Fish and Game
California State Water Resources Control
Board
Pueblo de Cochiti Department of Natural
Resources and Conservation
Colorado Department of Public Health
and the Environment
Connecticut Department of Environmental
Protection
Delaware Department of Natural Resources
Eastern Shoshone Tribe and Northern Arapaho
Tribe, Environmental Program
Florida Department of Environmental
Protection
Georgia Department of Natural Resources
Idaho Department of Environmental Quality
Illinois Environmental Protection Agency
Indiana Department of Environmental
Management
Iowa Department of Natural Resources
Lac Courte Oreilles Band of Lake Superior
Chippewa, Conservation Department
Lac du Flambeau Band of Lake Superior
Chippewa, Tribal Natural Resources
Department
Leech Lake Band of Ojibwe, Division of
Resource Management
Maine Department of Environmental
Protection
Maryland Department of Natural Resources
Massachusetts Department of Environmental
Protection -
Michigan Department of Environmental
Quality
Minnesota Pollution Control Agency
Mississippi Department of Environmental
Quality
Montana Department of Environmental
Quality
Nevada Division of Environmental Protection
New Hampshire Department of Environmental
Services
New Jersey Department of Environmental
Protection
New York State Department of Environmental
Conservation
North Dakota Department of Health
Ohio Environmental Protection Agency
Oklahoma Water Resources Board
Oregon Department of Environmental Quality
Pennsylvania Department of Environmental
Protection
Pyramid Lake Paiute Tribe
Rhode Island Department of Environmental
Management
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Sisseton-Wahpeton Sioux Tribe,
Environmental Program
South Dakota Department of
Environment and Natural Resources
Spirit Lake Nation, Tribal Environmental
Administration
Tennessee Department of Environment and
Conservation
Texas Commission of Environmental Quality
Turtle Mountain Band of the Chippewa
Indians Environmental Program
Utah Division of Environmental Quality
Vermont Department of Environmental
Conservation
Virginia Department of Environmental Quality
Washington Department of Ecology
West Virginia Department of Environmental
Protection
White Earth Band of Chippewa, Natural
Resources Department
Wisconsin Department of Natural Resources
The following people played a pivotal role and/or lent their expertise to the data analysis of this
project. These individuals painstakingly reviewed the dataset to ensure quality and consistency.
These NLA analysts included Neil Kamman (lead, on detail from VT Department of Environmental
Conservation), Richard Mitchell, and Ellen Tarquinio from EPA Office of Water; Phil Kaufmann, Tony
Olsen, Dave Peck, Spence Peterson, Steve Paulsen, Amina Pollard, John Stoddard, John Van Sickle
and Henry Walker from EPA Office of Research and Development; Donald Charles and Mihaele
Enache from the Academy of Natural Sciences, Philadelphia PA; Charles Hawkins from Utah State
University; Alan Herlihy from Oregon State University; Paul Garrison from WI Department of
Natural Resources; Jennifer Graham and Keith Loftin from U.S. Geological Survey, Lawrence, KS;
Jan Stevenson from Michigan State University, and Julie Wolin from Cleveland State University, OH.
EPA would also like to thank those people who lent their scientific knowledge and/or writing
talent to this report.
Contributors
Steve Heiskary, Minnesota Pollution Control Agency, MN; Neil Kamman, Department of
Environmental Conservation, VT; Terri Lomax, Department of Environmental Conservation, AK;
Alice Mayio, EPA Office of Wetlands, Oceans and Watershed, Washington, DC: Amy Smagula,
Department of Environmental Services, NH; Kellie Merrell, Department of Environmental
Conservation, VT; Leanne Stahl, EPA Office of Science and Technology, Washington, DC.
The National Lakes Assessment survey project was led by Susan Holdsworth (OW) and Steve
Paulsen (ORD) with significant programmatic help from Sarah Lehmann, Alice Mayio, Richard
Mitchell, Carol Peterson, Ellen Tarquinio, Anne Weinberg, and EPA Regional Monitoring Coordinators.
Contractor support was provided by individuals from Computer Sciences Corp., Dynamac Corp.,
EcoAnalysts, Inc., Great Lakes Environmental Center, Inc., Raytheon Information Services,
TechLaw, Inc. and Tetra Tech, Inc.
National Lakes/Assessment: A Collaborative Survey of the Nation's Lakes
-------
Additional NLA Reports and Information
To augment the findings of this report, EPA is providing two additional reports. The first
is the National Lakes Assessment - Technical Report. This report describes in detail the data
analyses and scientific underpinnings of the results. It is intended to aid States and other
institutions who would like a more in-depth explanation of the data analysis phase with the possible
intention of replicating the survey at a smaller scale. [The Technical Report, Field Methods and
Laboratory Protocols are currently available on EPA's web site at http ://www.epa.gov/owow/
lakes/lakessurvey/.] The second document is the National Lakes Assessment - Supplemental
Report. Due to a number of reasons, EPA is not able to report at this time the results from several
indicators (e.g., invasive species, sediment mercury, enterococci, and benthic macroinvertebrates).
Work is on-going for each of these indicators and results will be published when complete.
For those wishing to access data from the survey to perform their own analyses, EPA is making
flat files of the data available via the internet at the above address. Additionally, raw data and
information on the sampled lakes will be uploaded to EPA's STOrage and RETrieval (STORET)
warehouse at http://www.epa.aov/STORET.
National Lakes /Assessment: A i
vey of the Nation's Lakes
-------
Table of Contents
Acknowledgements i
Collaborators i
Contributors ii
Additional NLA Reports and Information iii
Tables and Figures vi
Executive Summary viii
Chapter 1. Introduction 2
A Highly Valued and Valuable Resource 2
Why a National Survey? 2
The National Aquatic Resource Surveys : 3
Chapter 2. Design of the Lakes Survey 8
Areas Covered by the Survey 8
Selecting Lakes 9
Lake Extent - Natural and Man-made Lakes 12
Choosing Indicators 12
Field Sampling 13
Setting Expectations 15
Chapter 3. The Biological Condition of the Nation's Lakes 20
Lake Health -The Biological Condition of Lakes 20
Stressors to Lake Biota 24
Ranking of Stressors 32
Chapter 4. Suitability for Recreation 36
Algal Toxins 36
Contaminants in Lake Fish Tissue 38
Pathogen Indicators 40
Chapter 5. Trophic State of Lakes 44
Findings For Trophic State 45
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapters. Ecoregional Results 48
Nationwide Comparisons 49
Northern Appalachians 52
Southern Appalachians 53
Coastal Plains 55
Upper Midwest 57
Temperate Plains 59
Southern Plains 61
Northern Plains 63
Western Mountains 65
Xeric 67
Chapter 7. Changes and Trends 72
Subpopulation Analysis of Change - National Eutrophication Study 73
Subpopulation Analysis - Trends in Acidic Lakes in the Northeast 74
Sediment Core Analysis of Change 76
Chapter 8. Conclusions and Implications for Lake Managers 81
Overall Findings and Conclusions 81
Implications for Lake Managers 83
Chapter 9. Next Steps for the National Surveys 91
Supplemental Reports... 92
Tools and Other Analytical Support 92
Future National Assessments 92
Acronyms 94
Glossary of Terms 95
Sources and References 99
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Tables and Figures
Table 1. World Health Organization thresholds of risk associated with
potential exposure to cyanotoxins 37
Table 2. Percent of U.S. lakes (natural and man-made) by trophic state,
based on four alternative trophic state indicators 45
Figure ES-1. Biological condition of lakes nationally and based on lake origin ix
Figure ES-2. Extent of stressor and relative risk of stressorto biological condition ix
Figure ES-3. Proportion of lakes from the 1972 National Eutrophication Study that exhibited change in
trophic status when compared to 2007 National Lakes Assessment x
Figure 1. The process of lake selection from NHD and the elimination of potential waterbodies for
sampling at various stages 10
Figure 2. Location of lakes sampled in the NLA 11
Figure 3. Size distribution of lakes in the U.S. overall and for natural and man-made lakes 12
Figure 4. NLA sampling approach for a typical lake 14
Figure 5. Reference condition thresholds used for good, fair, and poor assessment 16
Figure 6. Assessment of quality using the Planktonic 0/E Taxa Loss and Lake Diatom Condition
Index (Diatom IBI) for lakes nationwide, and for natural vs. constructed lakes 24
Figure 7. Phosphorus, nitrogen, and turbidity in three lake classes 25
Figure 8. Acid Neutralizing Capacity for Lakes of the U.S 26
Figure 9. Dissolved oxygen for lakes of the U.S 27
Figure 10. Schematic of a lakeshore 28
Figure 11. Lakeshore habitat for lakes of the U.S. as percent of lakes
in three condition classes 30
Figure 12. Shallow water habitat for lakes of the U.S. as percent of lakes
in three condition classes 30
Figure 13. Physical habitat complexity for lakes of the U.S. as percent of lakes
in three condition classes 31
Figure 14. Lakeshore disturbance for lakes of the U.S. as percent of lakes
in three condition classes 31
Figure 15. Relative extent of poor stressors conditions nationally and in
natural and man-made lakes 34
Figure 16. Percent of lakes in three algal toxin risk categories,
using three different indicators 38
Figure 17. Occurrence of microcystin in lakes 39
Figure 18. Percentage predator fish with mercury and PCB levels above and below
EPA recommend limits 40
Figure 19. Trophic state of lakes in the U.S 45
Figure 20. Ecoregions used as part of the National Lakes Assessment 48
National Lakes Assessment; A Collaborative Survey of the Nation's Lakes
-------
Figure 21. Biological condition of the nation's lakes across nine ecoregions based on planktonic
0/E taxa loss 49
Figure 22. Habitat condition of the nation's lakes across nine ecoregions based on lakeshore
habitat 50
Figure 23. Trophic state of the nation's lakes across nine ecoregions based on chlorophyll-a 51
Figure 24. Comparison of recreational risk of the nation's lakes across nine ecoregions, based on blue-
green algae levels corresponding to World Health Organization risk levels 51
Figure 25. NLA findings for the Northern Appalachian Ecoregion 53
Figure 26. NLA findings for the Southern Appalachian Ecoregion 54
Figure 27. NLA findings for the Coastal Plains Ecoregion 56
Figure 28. NLA findings for the Upper Midwest Ecoregion 58
Figure 29. NLA findings for the Temperate Plains Ecoregion 60
Figure 30. NLA findings for the Southern Plains Ecoregion 62
Figure 31. NLA findings for the Northern Plains Ecoregion 64
Figure 32. NLA findings for the Western Mountains Ecoregion '. 66
Figure 33. NLA findings for the Xeric Ecoregion 68
Figure 34. Proportion of NES lakes that exhibited improvement, degradation, or no change in
phosphorus concentration based on the comparison of the 1972 National Eutrophication
Survey and the 2007 National Lakes Assessment 74
Figure 35. Proportion of lakes that exhibited improvement, degradation, or no change in
chlorophyll-a concentration based on the comparison of the 1972 National Eutrophication
Survey and the 2007 National Lakes Assessment 74
Figure 36. Percentage and number of NES lakes estimated in each of four trophic classes
in 1972 and in 2007 based on chlorophyll-a concentrations 75
Figure 37. Change in percentage of lakes that are chronically acidic in the Adirondack Mountains
and New England 76
Figure 38. States with state-scale statistical surveys 85
Figure 39. Comparison of lakes by trophic state for Vermont, the Northern Appalachian
Ecoregion, and the contiguous U.S., based on chlorophyll-a 86
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Executive Summary
"A lake is the landscape's most beautiful
and expressive feature. It is earth's eye;
looking into which the beholder measures
the depth of his own nature."
These words by the American poet Henry
David Thoreau underscore America's love
of lakes. Lakes are places of reflection,
relaxation, and repose, but like all our
waters, they are being increasingly stressed.
Growing anthropogenic pressures have
prompted many governments, associations,
and individuals to invest time in preserving
or restoring the water quality of their lakes.
To protect our nation's lakes, Americans
must strive to understand how their actions
as individuals and as a society are affecting
them.
Under the Clean Water Act (CWA), the
U.S Environmental Protection Agency (EPA)
must report periodically on the condition of
the nation's water resources by summarizing
water quality information provided by the
states. However, approaches to collecting
and evaluating data vary from state to state,
making it difficult to compare the information
across states, on a nationwide basis, or over
time. EPA and the states are continually
working on ways to address this problem to
improve water quality reporting.
Congress, environmental groups,
and concerned citizens routinely ask EPA
about the quality of the nation's waters
with questions such as: What are the key
problems in our waters? How widespread are
the problems? Are there hotspots? Are we
investing in water resource restoration and
protection wisely? Are our waters getting
cleaner? To better answer questions about
1 The full report including technical supporting documents is available
on-line at http://www.epa.gov/owow/lakes/lakessurvev.
the condition of waters across the country,
EPA along with its state and tribal partners
have embarked on a series of surveys to be
conducted under the National Aquatic
Resource Surveys (NARS) program. This
relatively new program provides statistically
valid data and information vital to describing
water resource quality conditions across the
country and how these conditions vary with
geographic setting as well as human and
natural influences.
The National Lakes Assessment (NLA)
is one in a series of annual NARS surveys.
The NLA is the first statistical survey of
the condition of our nation's lakes, ponds,
and reservoirs.1 Based on the sampling of
over 1,000 lakes across the country, the
survey results represent the state of nearly
50,000 natural and man-made lakes that
are greater than 10 acres in area and over
one meter deep. In the summer of 2007,
lakes were sampled for their water quality,
biological condition, habitat conditions, and
recreational suitability. Field crews used the
same methods at all lakes to ensure that
results were nationally comparable. Analysts
analyzed the results against a reference
condition. Reference conditions were derived
from a set of lakes that were determined to
be the least disturbed lakes for a region.
-------
Key Findings
Biological Quality - 56% of the
nation's lakes are in good biological
condition. Natural lakes are more
than one-and-a-half times more
likely to be healthy than man-made
lakes (Figure ES-1).
Lake Physical Habitat - Of the
stressors included in the NLA, poor
lakeshore habitat is the biggest
problem in the nation's lakes; over
one-third exhibit poor shoreline
condition. Poor biological health
is three times more likely in lakes
with poor lakeshore habitat
(Figure ES-2).
Nutrients - About 20% of lakes
in the U.S. have high levels of
phosphorus and nitrogen. High
nutrient levels are the second
biggest problem in lakes. Lakes
with excess nutrients are two-and-a
half-times more likely to have poor
biological health (Figure ES-2).
Man-Mad* Lakes
20,238
| Good > <20% Taxa Lou Q Fur » 20% 40% Taxa Loss | Poor = >40'/ Taxa Loss
National Summary
56% Good
21% Fair
22% Poor
r
V.'v **>V - A
"i v'
'
*»
J-
Figure ES-1. Biological condition of lakes nationally and based on lake origin.
Extent of Stressor
LaKeshore Habitat
Physical Habitat Comptexity
Shallow Water Habitat
Total Nitrogen ^ 19 n
Total Phosphorus HH 182%
Lakeshore Disturbance
Turbidity 63%
Dissolved Oxygen
Numtxn
ul Lakes
17^07
16.033
9.9W
9467
9006
(.364
3.100
632
Relative Risk to
Biological Condition
0 20 40 60 tO 100
Percentage of Lakes Rated
Poor for Each Stressor
12345
Relative Risk
Figure ES-2. Extent of Stressor and relative risk of Stressor to biological condition.
-------
Algal Toxins - The NLA conducted the first-
ever national study of algal toxins in lakes.
Microcystin - a toxin that can harm humans,
pets, and wildlife - was found to be present in
about one-third of lakes and at levels of concern
in 1% of lakes.
Fish Tissue Contaminants - A parallel
study on fish tissue shows that mercury
concentrations in game fish exceed health
based limits in about half of lakes (49%);
polychlorinated biphenyls (PCBs) at potential
levels of concern are found in 17% of the lakes.
Trophic Condition - The NLA establishes
the first nationally consistent baseline of
trophic status. Over 36% of the nation's
lakes are mesotrophic, based on chlorophyll-a
concentrations.
Changes in Trophic Condition - When
compared to a subset of wastewater-impacted
lakes 35 years ago, trophic status improved in
one-quarter (26%) of those lakes (Figure ES-3).
This indicates that investments in wastewater
pollution control are working.
Change in Trophic State
(Chlorophyll)
Degraded
Unchanged
Improved
Figure ES-3. Proportion of NES lakes that exhibited improvement, degradation,
or no change in trophic state based on the comparison of the 1972 National
Eutrophication Survey and the 2007 National Lakes Assessment.
-------
Implications
As these results show, EPA and its state
and tribal partners have begun to answer
important national questions about the
condition of the country's lakes. The results
establish a national baseline status for future
monitoring efforts which can be used to track
scientifically credible trends in lake conditions.
Successive surveys will help answer the
question "Are our lakes getting better?"
For water resource managers,
policymakers, boaters, swimmers, and others,
the NLA findings suggest:
Our lakes are vulnerable to excess
human disturbances. This finding
supports reports from state lake
management programs which
increasingly report that development
pressures on lakes are steadily
growing.
Poor habitat condition imparts a
significant stress on lakes and could
suggest the need for stronger
management of lakeshore
development.
Managers, residents, businesses, and
community leaders should work together and
enhance their efforts to preserve, protect,
and restore their lakes and the natural
environment surrounding them.
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
CHAPTER I.
INTRODUCTION
IN THIS CHAPTER
A Highly Valued and Valuable Resource
Why a National Survey?
The National Aquatic Resource Surveys
-------
Chopter / Introduction
Chapter 1
Introduction
A Highly Valued and
Valuable Resource
For anyone who went fishing as a child,
water-skiing as a teen, or bird-watching as
an adult, lakes are special places. Healthy
lakes enhance the quality of life. In addition
to supplying people with essential needs
like drinking water, food, fiber, medicine,
and energy, a lake's ecosystem is important
in providing habitat for wildlife, recreation,
aesthetics, reducing the frequency and
severity of floods, shaping landscapes, and
affecting local and regional climates. Lakes
provide habitat for wildlife and enjoyment for
people while supporting intrinsic ecological
integrity for all living things.
It is difficult to put a price on a natural
treasure. Certainly, from a vacationer's
perspective, lakes are invaluable, providing
endless enjoyment and relaxation year-
round. According to the U.S. Fish and
Wildlife Service, 30 million Americans went
fishing in 2006 and $30 billion was spent on
recreational fishing. Locally, this translates
into important economic and recreational
benefits. For example, Lake Champlain,
on the border of Vermont and New York,
has over 65 beaches and 98 fishing-related
businesses. According to the 2003 Lake
Champlain Management Plan, in 1998 a total
of $3.8 billion was generated from tourism.
As more and more people use lakes for their
livelihood, the competition for lake resources
will continue.
Protecting lake ecosystems is crucial
not only to protecting this country's public
and economic health, but also to preserving
and restoring the natural environment for
all aquatic and terrestrial living things.
Lake protection and preservation can only
be achieved by making informed lake
management policy decisions at and across all
jurisdictional levels.
Why a National Survey?
Water resource monitoring in the U.S.
has been conducted by many different
organizations over many decades using
a variety of techniques. States and tribes
conduct monitoring to support many Clean
Water Act (CWA) programs. Section 305(b)
of the CWA requires the U.S Environmental
Protection Agency (EPA) to report periodically
on the condition of the nation's water
resources by summarizing information
provided by the states. Yet approaches
to collecting and assessing data vary from
state to state, making it difficult to compare
the information across states or on a
nationwide basis. Each of these monitoring
efforts provides useful information relative
to the goals of the individual programs, but
integrating the data to form a nationwide
assessment has been difficult.
-------
Chapter I Introduction
In recent years, a number of reports
have identified the need for improved
water quality monitoring and analysis at a
national scale. Among these, the General
Accounting Office (2000) reported that
EPA and states cannot make statistically
valid assessments of water quality and
lack the data to support key management
decisions. The National Research Council
(2001) recommended that EPA and states
promote a uniform, consistent approach
to water monitoring and data collection to
better support core water management
programs. The National Academy of Public
Administration, in their 2002 report entitled:
Understanding What States Need to Protect
Water Quality, concluded that improved
water quality monitoring is necessary to help
state agencies make better decisions and use
limited resources more effectively. These
reports underscore the need for more efficient
and cost-effective ways to understand the
magnitude and extent of water quality
problems, the causes of these problems, and
practical ways to address the problems.
The National Aquatic
Resource Surveys
To bridge this information gap, EPA,
other federal agencies, states and tribes
are collaborating to provide the public
with improved environmental information.
Statistical surveys are one way of addressing
water resource assessment needs. By
choosing a statistical design with standardized
field and laboratory protocols, the EPA, states
and tribes are able to analyze data that are
nationally consistent and representative
of waterbodies throughout the U.S. These
statistical surveys offer a cost-effective and
scientifically valid way to fulfill statutory
requirements, complement traditional
monitoring programs, and support
a broader range of management decisions.
The surveys are designed to answer such
questions as:
What is the extent of waters that
support a healthy biological condition,
recreation, and fish consumption?
How widespread are major stressors
that impact water resource quality?
Are we investing in water resource
restoration and protection wisely?
Are our waters getting cleaner?
State Water Quality Reports
Under section 305(b) of the Clean
Water Act the states must submit
biannual reports on the quality of
their water resources. According
to the most recently published
National Water Quality Inventory
Report, 2004, the states assessed
little over a third of the nation's
waters 37% or 14.8 million acres
of the nation's 40.6 million acres
of lakes, ponds and reservoirs.
Of the lakes that were assessed,
over half, 58% or 8.6 million
acres, were identified as impaired
or not supporting one or more
of their designated uses such as
fishing or swimming. The states
cited nutrients, metals (such as
mercury), sewage, sedimentation
and nuisance species as the top
causes of impairment. Leading
known sources of impairment
included agricultural activities and
atmospheric deposition, although
for many lakes, the sources of
impairment remain unidentified.
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter
Introduction
To help fulfill the need for nationwide
statistical surveys, the National Aquatic
Resources Survey (NARS) program was
established in 2005. The specific goals of
NARS are to generate scientifically valid
information on the condition of water
resources at national and ecoregional scales,
establish baseline information for future
trends assessment, and assist states and
tribes in enhancing their water monitoring and
assessment programs. The focus of NARS
is on lakes as groups, or populations, rather
than individual lakes. For example, a local
lake manager and perhaps a state manager
will be interested in Lake Okeechobee,
Florida, and the changes it has experienced
in nutrients over the past 30 years. The
NARS assessments will focus more on the
percentage of all lakes that have experienced
changes in nutrient status over time. This is
similar to public health where an individual
and their physician track that person's weight,
whereas national public health policy is driven
more by the percentage of people in the
country that are classified as obese.
The national statistical surveys and other
statistical surveys have begun to provide
answers to water resource questions with
a known level of confidence. Working with
its partners in states, tribes, territories, and
other federal agencies, EPA has in recent
years conducted statistical surveys of coastal
waters, rivers and streams, and contaminants
in lake fish tissue. The agency's plans are
to survey each of the five waterbody types,
(lakes, rivers, streams, wetlands, and
estuaries), on a 5-year rotating basis. EPA
and its partners anticipate that the national
surveys will continue to foster collaboration
across jurisdictional boundaries, build state
and tribal infrastructure and capacity for
enhanced monitoring efforts, and achieve
a robust set of statistically-sound data for
better, more informed water resource quality
management policies and decisions.
The National Lakes Assessment (NLA)
is one component of the National Aquatic
Resource Surveys. This report summarizes
the first-ever assessment of lakes across the
continental United States using consistent
protocols and a modern, scientifically-
defensible statistical survey approach.
Because of their scientific credibility,
results from these surveys are being used
in other scientific contexts. Most notably
is the recent Heinz Center Report; The
State of the Nation's Ecosystems, 2008.
The Heinz Center's report is designed to
provide a high level, comprehensive and
scientifically sound account on the state
of the nation's ecosystems. The Heinz
Center uses data derived from EPA's
Wadeable Streams Assessment report
and National Coastal Conditions Report
in answering a number of outstanding
questions about surface water health
in our country. Information from on-
going and upcoming national surveys will
help fill gaps identified for other water
resources and show trends in national
water quality.
National Lakes Assessment. A Collaborative Survey oftlte Nation's Lakes
-------
HIGHLIGHT
Think Globally - - Act Locally.
Restoring Mousam Lake
"Every little bit helps," is perhaps the fundamental tenet
of the estimated 3,000 to 4,000 local watershed groups
across the country. Many communities are proving that
they can make a noticeable difference in their neighborhood
water resource. In York County, Maine, the Soil and Water
Conservation District (SWCD) and the Mousam Lake Regional
Association (MLRA) together with residents, townships, state
agencies and others embarked on the Mousam Lake Water
Quality Improvement Project. With widespread collaboration
and a little bit of funding, they were able to clean up an
impaired lake.
Confronting Environmental Challenges
Mousam Lake, a 863-acre lake located at the southern
point of Maine, is a popular spot for boaters, anglers, and
vacationers with its sandy shores and excellent cold and
warm water trout fisheries. However, this 21- square mile
watershed suffered from suburbanization and the conversion
of forested land to driveways and parking lots. The lake's
shoreline is heavily developed with over 700 seasonal and
year-round homes and a heavily used boat ramp. For the past
several decades, Mousam Lake has endured increased soil erosion and pollution from stormwater runoff
from home construction, lawns, roads, and failing septic systems. Higher levels of phosphorus has led to
increased algal growth, decreased water clarity and lower levels of dissolved oxygen. In the 2003 Total
Maximum Daily Load (TMDL) assessment, excess phosphorus was identified as the major impairment. This
downward trend in water quality resulted in a steady decline in the lake's once viable ecology and that of
its surrounding aquatic habitats. Maine's Department of Environmental Protection (MDEP) attributes the
problem to soil erosion and polluted runoff from residential properties and camp roads and effluent from
inadequate septic systems located in the sandy soils around the lake. The TMDL assessment estimated
that to meet Maine water quality standards, the annual amount of phosphorus reaching the lake would
need to be reduced by 27%.
A Decade of Effort
Since 1997, the York County SWDC, MLRA, MDEP, and the towns of Acton and Shapleigh have
been working together to address sources of pollution in Mousam Lake and foster long-term watershed
stewardship. In 1999, the Mousam Lake Water Quality Improvement Project began. With help from EPA,
the Maine Department of Transportation and the Maine Department of Agriculture, negotiated cost share
agreements with public and private landowners and best management practices were initiated at 45
priority sites. Technical assistance was provided to another 77 landowners. Projects included stabilizing
shoreline erosion, improving gravel road surfaces and installing and/or upgrading roadside drainages.
Twenty-one roads were repaired. In 2001, the Lake Youth Conservation Corps program was established to
help with the implementation of best management practices, raise local awareness and commitment
Mousam Lake Watershe
\ U
National Lakes Assessment A Collaborative Survey of the Nation's Lakes
-------
to lake protection, and involve local youth in environmental stewardship. Since 2007, the youth have
completed over 115 projects and continue to repair an average of 18 sites each year with annual
support from the towns of Acton and Shapleigh. The total cost for the project was $1.1 million with local
townspeople and others contributing over $400,000 in matching funds or in-kind services.
A Cleaner, Healthier Lake
In 1998 MDEP designated Mousam Lake as impaired and added it to the state's section 303(d) list of
waters not meeting water quality standards, a requirement of the federal Clean Water Act. From 1999
through 2006, a galvanized community tackled the problem and in 2007, monitoring results indicated that
pollution loads in the lake were reduced by more than 150 tons/per year of sediment and 130 pounds/
per year of phosphorus. Water clarity depth has increased by a full meter from what it was in the lake ten
years ago. Today, erosion control projects continue thus keeping an estimated 76 tons of sediment and
64 pounds of phosphorus out of the lake each year. In 2006, Mousam Lake was removed from the state's
303(d) list of impaired waters.
Staff and a small cadre of local leaders are continuing their campaign to keep the lake in good health.
Community outreach and education activities are ongoing to inform residents on how they can help.
As part of the project, numerous newsletters have gone to every household in the watershed; MLRA
holds annual meetings; the SWCD conducts workshops and delivers presentations; 30 construction sites
have been acknowledged with "Gold Star" signs for environmental stewardship; and more than 200
homeowners attended one of the thirteen "Septic Socials" to learn about septic system function, proper
maintenance and water conservation.
Every Little Bit Helps
In many, many instances, small, local efforts can provide incentives and moral support for others.
The success of the Mousam Lake project has inspired protection efforts on several neighboring lakes. The
Acton Wakefield Watershed Alliance, the Square Pond Association, and the Loon Pond Association are
now busy with their own restoration activities. For more
information or tips from the people at Mousam Lake,
contact Joe Anderson at York County SWCD at (207)
324-0888, janderson@yorkswcd.org or Wendy Garland
(MDEP) at (207) 822-6320, wendy.garland@maine.gov.
Vegetated buffer planting by Master Gardeners.
National Lakes Assessment A Collaborative Survey of the Nation's Lakes
-------
CHAPTER 2.
DESIGN OF THE LAKES SURVEY
IN THIS CHAPTER
Areas Covered by the Survey
Selecting Lakes
Lake Extent - Natural and Man-Made Lakes
Choosing Indicators
Field Sampling
Setting Expectations
-------
Chapter 2
Design of the Lakes Survey
Chapter 2
Design of the Lakes Survey
Lakes in the U.S. are as varied and
unique as the landscape surrounding them.
Receding glaciers formed thousands of lakes
in the northwestern, upper midwestern, and
northeastern parts of the country. Glacial
action formed the Finger Lakes in New York,
the Adirondack region, the kettle ponds in
New England, as well as numerous lakes
and "prairie potholes" located in Minnesota,
Wisconsin, Iowa, and the Dakotas. In
contrast, Oregon's Crater Lake is a water-
filled volcanic depression, as is Yellowstone
Lake in Wyoming. Lake Tahoe in California
and Pyramid Lake in Nevada were formed
by tectonic action. Along major rivers, like
the Mississippi, oxbow lakes were formed
from meandering river channels. Similarly,
damming of the Columbia River and the
Colorado River has created large man-made
lakes and reservoirs. Smaller previously
impounded streams comprise thousands of
man-made lakes that provided energy for
mills during industrialization. Natural lakes
are scarce across the southern U.S. Many of
the lakes in the arid southwestern
and the humid southeastern U.S.
are man-made lakes or reservoirs.
The NLA survey included examples
of all of these lake types.
Areas Covered By
the Survey
The NLA encompasses the
lakes, ponds and reservoirs of
the continental U.S. This land
comprising the lower 48 states
includes private, state, tribal
and federal land. Although not
included in this report, a lake-
sampling project is underway in
Alaska. It should also be noted
that Hawaii does not have any lakes
and thus was not included. Information from
the NLA is also presented both for natural and
man-made lakes because of the expectation
that natural and man-made lakes might be
of different biological condition or respond to
stressors in different ways.
NLA results are reported for the
continental U.S. and for 9 ecological regions
(ecoregions). Areas are included in an
ecoregion based on similar landform and
climate characteristics (see Chapter 6 and
Figure 20). Assessments were conducted
at the ecoregion level because the patterns
of response to stress are often best
understood in a regional context. Some
states participating in the NLA assessed
lake condition at an even finer state-scale
resolution than the ecoregional scale by
sampling additional random sites within their
state boundaries. Although these data are
included in the analysis described in this
report, state-scale results are not presented.
-------
Chapter 2 Design of the Lakes Survey
"
Alaska's Lake Assessment
The State of Alaska is about one-fifth the land mass of the continental U.S. Most of
it is sparsely populated with extremely limited access. This limited access has helped
preserve its rugged beauty and abundant natural resources. But Alaska is facing
pressure from climate change and natural resource development. In the populated
areas, the main causes for waterbody pollution are urban runoff and agricultural activity.
There are an estimated 3 million lakes in Alaska. Instead of being a full participant in the National Lakes
Survey, the State of Alaska opted to conduct a regional assessment. It focused on the Cook Inlet Basin, an
area located in the southcentral part of the state, and at 39,325 Square miles, is slightly smaller than the
state of Kentucky. The State selected this area because the only agricultural activity of significance occurs
within the Cook Inlet Basin.
Alaska's lake assessment began in 2007 with a pilot study of four lakes. This pilot study was focused
on access and coordinating logistics of sampling, procedures, and analysis. In 2008, the full project was
completed with sampling of 50 lakes in the Cook Inlet ecoregion. The field crew was from the Alaska
Department of Environmental Conservation and the University of Alaska Anchorage Environment & Natural
Institute. In addition to the National Lakes Assessment indicators, fish-tissue for metals and mercury,
sediment trace metals, and core dating were added to the study.
To date, all water chemistry, habitat, and lake profile data has been analyzed. Biological indicators,
sediment metals and mercury, and fish tissue samples are currently being analyzed. All data collected must
undergo quality assurance review before a final release of the data. However, initial results indicate that lakes
in the Cook Inlet ecoregion of Alaska are healthy.
Selecting Lakes
Since a census of every lake in the
country is cost prohibitive and beyond the
reach of any program, EPA used a statistical
sampling approach incorporating state-of-
the-art survey design techniques developed
by its research program. The first step,
to ascertain the number of lakes in the
country, was challenging because there is no
comprehensive list or source for all lakes in
the U.S. The best resource available is the
USGS/EPA National Hydrography Dataset or
NHD. The NHD is a multi-layered series of
digital maps that reveal topography, area,
flow, location, and other attributes of the
nation's surface waters. When queried,
NHD has 389,005 features listed that could
potentially be lakes, ranging in size from less
than 1 hectare (2.4 acres) up to the largest
lakes in the country. Many were excluded
at the outset for a number of reasons, such
as being a wetland. Figure 1 illustrates the
sample framework for the survey.
Initial discussion by states and EPA
regarding the scope of the survey focused on
the size of lakes that were to be considered
in the target population. It was agreed that,
to be included, the site had to be a natural or
man-made freshwater lake, pond or reservoir,
greater than 10 acres (4 hectares), at least
3.3 feet (1 meter) deep, and with a minimum
of a quarter acre (0.1 hectare) open water.
The Great Lakes and the Great Salt Lake
National Lakes Assessment. A Collaborative Survey of the Nation's Lakes
-------
Chapter 2 Design of the Lakes Survey
National Hydrography Dataset (NHD) - 389.005
were not included in the survey, nor were
commercial treatment and/or disposal ponds,
brackish lakes, or ephemeral lakes. After
applying the criteria, 68,223 waterbodies
were considered lakes by the NLA definition
and thus comprised the target population.
Other factors in lake selection included
accessibility. In some cases, crews were
either denied permission by the landowner or
unable to reach the lake for safety reasons,
such as sharp cliffs or unstable ridges. Using
data from the crews' experience, it was
estimated that 27% or 18,677 lakes fell into
this category. This leaves 49,546 lakes the
NLA data is able to assess which is called the
inference population. In the end, a total of
909 lakes were sampled in the survey. These
909 lakes will represent the population. For
quality assurance purposes, 10%, or 91,
of the target lakes were randomly selected
for a second sampling later in the summer,
bringing the total sampling incidents to 1,000.
Because of the selection process, the sampled
NLA lakes represent 49,546 lakes or 73%
of the target population. Thus, throughout
this report, percentages reported for a given
indicator are relative to the 49,546 lakes. For
example, if the condition is described as poor
for 10% of lakes nationally, this means that
the number of lakes estimated to be poor for
that indicator is 4,955 lakes. As an added
feature, some of the survey sites were part
of EPA's 1972 National Lake Eutrophication
Study (NES).
Excluded - less than
4 hectares -233.627
Excluded - other - 32.009
Included - 123.369
NHO Sample Frame -123,369
Non-Target (not a lake)
55,146
Target - meets target
population definitions 68.223
Target Population - 68,223
Target - not sampled
18,677
Target - Sampled 49,546
Inference Population -49,546 Lakes
Figure 1. The process of lake selection from NHD and the
elimination of potential waterbodies for sampling at various
By including this subset of lakes EPA
hoped to be able to evaluate changes that
occurred between the 1970s and 2007.
In conjunction with the national survey, a
number of states opted to sample additional
lakes to achieve a state-wide probabilistic
survey. EPA provided a list of additional lakes
to the states so that any state wishing to
conduct a state-scale statistical survey could
do so. Sampling and processing methods
from these additional lakes had to adhere
to both the national field and laboratory
protocols. Nine states (MI, WI, IN, MN,
TX, OK, ID, OR and WA) took advantage
of the opportunity and the results from the
additional sites were analyzed along with the
national data. Some states increased the
number of sites, but only collected a subset of
indicators. Still other states opted to expand
the list of indicators to address issues specific
to their state; for example, Minnesota used its
state-scale survey to assess pesticides.
-------
Chapter 2 Design of the Lakes Survey
Figure 2 shows the location of the lakes
that were sampled for the NLA. In total,
1,028 lake sites were sampled and included
in the survey estimates (909 national target
sites; 119 state added sites). The surveyed
lakes cover an area of 3.8 million acres of
surface water spread across the national
landscape.
The site selection for the survey ensures
that EPA can make unbiased estimates
concerning the health of the waters
throughout the nation with statistical
confidence. The greater the number of
sites sampled, the more confidence in the
results. The number of sites included in
the survey allows EPA to determine the
percentage of lakes nationwide and within
predetermined ecoregions that exceed a
threshold of concern with 95% confidence.
In the graphs throughout this report, the
margin of error is provided as thin lines on
either side of the bars and represent the
95% confidence interval for the estimate.
For national estimates, the margin of error
around the NLA findings is approximately
±5% and for ecoregions the margin of error is
approximately ±15%.
m *~ « it
v *r f * *r i
' -trv J. *\% :\vA
NLA Sampled Sites
Figure 2. Legation of lakes sampled in the NLA.
-------
Chapter 2
Design of the Lakes Survey
Lake Extent -
Natural arid Man-made Lakes
NLA analysts, comprised of lake science
experts both within and outside the Agency,
carefully examined available records for each
sampled lake to determine its origin, using
the guideline that lakes that existed
pre-European settlement are considered
natural, even if presently augmented
by means of an impoundment or other
earthworks. Using this operational
definition, 41% of the estimated 49,546
lakes are man-made reservoirs, while
59% are of natural origin. This means
that nearly one-half of today's lakes
were not here when the colonists
arrived.
Natural
(29,308)
Natural lakes come in many
different sizes and man-made lakes
do as well. While many people hold
the image of man-made lakes as large
reservoirs, most man-made lakes are
relatively small. A total of 52% of
man-made lakes are 10-25 acres (4-10
hectares) in size compared with only
34% of the natural lakes in that small
lake size category. Large lakes, over
12,500 acres (5,000 hectares), are
rare in the U.S., comprising only 0.3%
of natural lakes and 0.6% of man-made lakes
(Figure 3).
Choosing Indicators
Scientists and lake managers recognize
that lake ecosystems are dynamic and
indicators selected to characterize lakes must
represent important aspects of water resource
quality. For the NLA, a suite of chemical,
physical and biological indicators were chosen
to assess biological integrity, trophic state,
recreational suitability, and key stressors
impacting the biological quality of lakes.
Man-Made
(20,238)
Lake Size
Mum bet
of Lakes
10-25 acres
25-125 acres
125-250 acres
250-1 250 acres
1.250-12.500 acres
> 12 500 acres
20 40 60 80
Percentage of Lakes
100
Figure 3. Size distribution of lakes in the U.S. overall and for
natural and man-made lakes.
Although there are many more indicators
and/or stressors that affect lakes, NLA
analysts believe these to be the most
representative at a national scale. The
NLA survey marks the first time all these
indicators have been applied consistently and
simultaneously to lakes on a national scale.
-------
Chapter 2 Design of the Lakes Survey
Biological
Recreational
Water Quality
Physical Habitat
Sediment diatoms
Phytoplankton (algae)
Zooplankton
Benthic
macroinvertebrates*
Pathogens* (enterococci)
Algal toxin (microcystins)
Algal cell counts
(Cyanobacteria)
Algal density
(chlorophyll-a)
Sediment mercury*
Nutrients
(phosphorus & nitrogen)
Water column profile
(dissolved oxygen,
temperature, pH, turbidity,
acid neutralizing capacity,
salinity)
Algal density
(chlorophyll-a)
Lakeshore habitat
cover and structure
Shallow water habitat
cover and structure
Lakeshore human
disturbance
Invasive species*
* These indicators are still under evaluation and are not included in this report. A supplemental report will be issued with these results.
For this survey, NLA analysts used
phytoplankton and zooplankton as the main
biological endpoints for lake condition.
Diatoms, a type of phytoplankton, are also
used to look at biological condition. To
address recreational/human health related
concerns, the NLA looked at actual levels
of the algal toxin, microcystin, along with
cyanobacterial cell counts and chlorophyll-a
concentrations as indicators of the potential
for the presence of algal toxins. Although fish
samples were not collected in the survey,
NLA analysts also looked at the findings of a
parallel study of contaminants in fish tissue.
For the NLA, cyanobacteria levels are used
as the primary end point for recreational
condition. Chlorophyll-a was used to assess
trophic status.
Both physical and chemical stressor
indicators were measured. Shorelines affect
biological communities in many ways, such
as providing food and shelter for aquatic
wildlife, and by moderating the magnitude,
timing, and pathways of water, sediment, and
nutrient inputs. Shorelines also buffer the
lake from human activities. Water quality
characteristics, such as nutrient levels and
dissolved oxygen, create environments
essential for aquatic organisms to survive
and grow. At the bottom of the lake,
sediment diatoms, a type of algae that live
on the bottom and leave fossil remains,
allow examination of current water quality
conditions, such as phosphorus levels, along
with historical conditions. These indicators
were selected because water quality stressors
impact the biological health of lakes- from
primary producers (phytoplankton or algae)
to small openwater animals (zooplankton) to
macroinvertebrates (insects, mollusks and
crustaceans) and fish.
Field Sampling
In preparation for the survey, each target
lake was screened to verify that it met the
inclusion criteria. Throughout the summer
of 2007, 86 field crews, consisting of 2 to 4
people each, sampled lakes from Maine to
California. To ensure consistency in data
collection and quality assurance, the crews
attended a three-day training session, used
standardized field methods and data forms,
and followed strict quality control protocols
including field audits.
-------
Chapter 2 Design of the Lakes Survey
At each lake site, crews collected samples
at a single station located at the deepest
point in the lake and at ten stations around
the lake perimeter (Figure 4). At the mid-
lake station, depth profiles for temperature,
pH, and dissolved oxygen were taken with
a calibrated water quality probe meter or
multi-probe sonde. A Secchi disk was used
to measure water clarity and depth at which
light penetrates the lake or the euphotic
zone. NLA analysts used these vertical
profile measurements to determine the
extent of stratification and the availability
of the appropriate temperature regime
and level of available oxygen necessary
to support aquatic life. Single grab water
samples were collected to measure nutrients,
chlorophyll-a, phytoplankton, and the algal
toxin microcystin. Zooplankton samples
were collected using a fine mesh (80um) and
course mesh (243um) conical plankton net.
A sediment core was taken to provide data on
sediment diatoms and mercury levels. The
top and bottom layer of the sediment core
was analyzed to detect
possible changes in
diatom assemblages
over a period of time.
Along the perimeter
of the lake, crews
collected data and
information on the
physical characteristics
that affect habitat
suitability. Information
Figure 4. NLA sampling approach for a typical lake. Sampling locations are denoted by letters A-J and Z. Riparian, littoral, sublittoral,
and profundal lake zones are depicted, as is the schematic design of a shoreline physical habitat station.
-------
Chapter 2 Design of the Lakes Survey
on substrate composition was recorded
along ten predetermined stations. Benthic
macroinvertebrates, collected with a SOOum
D-frame net, and water samples for pathogen
analysis were collected at the first and last
station, respectively. Filtering and other
sample preparations took place back on
shore. Sampling each lake took a full day and
many crews spent weeks in the field. At the
end of the season, field crews collected 8,536
water and sediment samples; took over 5,800
direct measurements, and recorded in excess
of 620,000 observations.
Setting Expectations
Selecting Reference Lakes
In order to assess the condition of the
country's lakes, findings were compared to
conditions in a suite of "reference lakes".
A reference lake in the NLA is a lake (either
natural or man-made) with attributes (such as
biological or water quality) that come as close
as practical to those expected in a natural
state, i.e., least-disturbed lake environment.
NLA analysts used the reference distribution
as a benchmark for setting thresholds for
good, fair, and poor condition for each of the
indicators.
EPA's experience with past surveys
showed that only a small portion of the
sampled population of lakes will be of
reference quality. EPA used both hand-picked
lakes that were thought to be of high quality
as well as high quality lakes from the random
site selection process to serve as candidate
reference lakes that might ultimately serve as
"least-disturbed" benchmark reference sites.
The candidate lakes were sampled identically
to, and in addition to the core target lakes.
Subsequently, data results from all sampled
lakes (target and hand-selected) were
evaluated against the reference screening
criteria to determine the final set of lakes that
would be used to characterize the reference
condition. NLA analysts used a number
of independent variables reflecting human
influence as classification and screening
criteria, e.g., limnological shoreline index,
chloride content, total water column calcium,
and others. Two parallel groups of reference
lakes were set; one for biological condition,
and another for nutrient stressors. The later
set of sites was developed so that nutrient
levels could be used in screening reference
lakes for biological condition.
When considering reference condition, it
is import to remember that many areas in the
United States have been altered, with natural
landscapes transformed by cities, suburban
sprawl, agricultural development, and
resource extraction. To reflect the variability
across the American landscape, these least-
disturbed lakes diverge from the natural state
by varying degrees. For example, highly
remote lakes like those in the upper elevation
wilderness areas of Montana may not have
changed in centuries and are virtually
pristine, while the highest quality, least-
disturbed lakes in other parts of the country,
especially in urban or agricultural areas, may
exhibit different levels of human disturbance.
The least-disturbed reference sites in these
widely influenced watersheds display more
variability in quality than those in watersheds
with little human disturbance. Thus in
reference conditions across the country, the
-------
Chapter 2 Design of the Lakes Survey
"bar" for expectations may be different.
The resulting reference lakes represent the
survey team's best effort at selecting lakes
that are the least disturbed nationally in
specific areas across the country.
Thresholds - Good, Fair, and Poor
After the reference lakes were selected
and reference condition was determined,
thresholds against which the target lakes are
compared were set. Two types of assessment
thresholds were used in the NLA. The first
is fixed thresholds. Fixed thresholds are
based on longstanding accepted values
from the peer reviewed scientific literature.
They are well established, and widely and
consistently used. An example of this is
standard chlorophyll-a thresholds which are
used to classify lakes into the different trophic
categories.
The second type of threshold type is based
on the distribution (i.e., the range of values)
of a particular indicator derived from the
reference lakes data. For NLA, each indicator
for a lake was classified as either "good",
"fair" or "poor" condition relative to the
conditions found in reference lakes. That is,
"good" denotes an indicator value similar to
5% of reference distribution
25% of reference distribution
Target Lake
Distribution
Reference Lake
Distribution
Low
Indicator Score
(e.g. Biological Condition)
High
that found in reference lakes, "poor" denotes
conditions definitely different from reference
conditions, and "fair" indicates conditions
on the borderline of reference conditions.
Specifically, these thresholds are then applied
to the results from the target lakes and are
classified as follows: lake results above 25%
of the reference range values are considered
"good;" below the 5% of the reference
range value are "poor;" and those between
the 5% and 25% are "fair" (Figure 5).
These designations are not intended to be a
replacement for the evaluation by states and
tribes of the quality of lakes relative to the
concept of specific designated uses.
Figure 5. Reference condition thresholds used for good,
fair, and poor assessment.
-------
HIGHLIGHT
Surveying the Nation's Lakes for
Invasive Aquatic Species
Amy P. Smagula
New Hampshire Department of Environmental Services
Invasive species have long been purported as the next great environmental crisis on a national and
even global scale. On every continent in nearly all aquatic habitat types, at all levels of the food web,
invasive species have made an impact. Invasive aquatic species (also termed exotic or introduced species)
can be described as those species that live in water but are generally not native to a particular waterbody.
In general they have traits or characteristics that suggest a competitive ecological advantage over native
species. Invasive species grow rapidly and/or aggressively, so
that they can eventually dominate a habitat to the detriment of
native creatures that already live there. Invasive aquatic species
include a whole range of organisms, including plants, animals,
pathogens, and others.
Grow very quickly and occupy
large areas in a short timeframe;
Have various strategies for
reproduction;
Survive in a range of conditions;
Have no natural predators to
control them;
Take over areas from native
plants/animals and can thus
be ecologically devastating;
Pose serious economic problems
in terms of control costs and costs
attributable to habitat loss and
recreational impairments to
waterbodies, including reductions
in property values on infested
waterbodies;
Are very difficult if not impossible
to control; and
Threaten nearly half of the species
listed under the Endangered
Species Act.
The types of invasive aquatic species in our lakes are
numerous and diverse, and can include aquatic plants that either
root in substrate (like Eurasian watermilfoil or Hydrilla) or that
float on the surface of the water (like the giant salvinia). They
include larger animals such as fish (like the snakehead fish), and
macroinvertebrates (like the zebra mussel). They also include
those seen only with the aid of a microscope, such as exotic
algae or the spiny water flea.
The pathways for invasive aquatic species introductions are
varied, and include ballast water discharges from large vessels,
retail industries like the aquarium and home water garden
trades, and even internet suppliers of aquatic species. Once a
species becomes established in a waterbody, either by accidental
(e.g., contaminated boat) or intentional means (e.g., dumping
of an aquarium or direct planting), it is transient recreational
equipment (motor boats, kayaks, diving gear, etc.) that causes
the lake-to-lake spread of these species.
Depending on the point of introduction and transport
pathways, species can become widely distributed or remain
as localized infestations. Unfortunately, many invasive aquatic
species are highly adaptive, and can survive and thrive in a wide range of environmental conditions. Big
or small, plant or animal, invasive aquatic species in our lakes can have detrimental effects on the very
attributes of those waterbodies that scientists, citizens, and environmental stewards are trying to
evaluate and preserve.
How Can Data from the NLA Survey Help?
One of the goals of the National Lakes Assessment (NLA) is to help citizens and government entities
have current information on the health of our lakes so that they can take action to prevent further
degradation. Data on invasive aquatic species can be used to help determine which of these species has
been documented in a state or region, and if those are well established populations or if they are
National Lakes Assessment A CoHoborotive Survey of the Nation's Lakes
17
-------
pioneering and can be eliminated or halted before other waterbodies in the area are affected. These
data may also be used to assist with risk assessments for an area, based on what has been found in
neighboring states, coupled with tourism and recreational data for that region.
The Key \s Prevention, Early Detection, & Rapid Response
Preventing the introduction of invasive aquatic species, is paramount to protecting a waterbody. Many
states and regional working groups have established education campaigns to alert lake users and others
about the threats posed by invasive aquatic species and to hopefully prevent a new infestation by proper
care of transient recreational vessels and gear. Additionally, many states have developed prohibited
species lists in an effort to prevent overland transport and sale of these invasive species.
When prevention fails and an infestation does occur, early detection is critical. Individual lake
associations, special interest groups, and other such entities are encouraged to look for new infestations
on a regular basis during the growing season, particularly if they live on a waterbody that receives a high
level of use by transient boaters. A small new infestation is much more easily contained or eradicated
than a dense and large-scale infestation. A network of volunteer monitors around a waterbody can look
for signs of invasive species and report to key officials who can effectively deal with a potentially new
infestation.
State officials should be knowledgeable and poised for a rapid response to contain and control an
infestation. They should be aware of appropriate management actions for the species in question and how
to best approach the problem. Fortunately many states have developed specific plans for aquatic nuisance
species management, so that an immediate response can be made.
Hydrilla
(Hydrilla verticillata)
First Identified in US: 1960
Native Range: Africa
U.S. Distribution: WA, CA, AZ, TX, IA, LA, MS, AL, TN, FL,
GA, SC, NC, VA, DE, PA, CT, MA, ME
Description: Narrow leaves whorled around the 20 ft main
stem. It is the most invasive submergent plant in the U.S., and
can even out-compete invasive watermilfoil by canopying over
the surface. It has been observed to grow up to a half-inch per
day in optimum conditions.
Impacts: This plant forms thick impenetrable growth in the
water column of lakes. It can impact native aquatic plants and
animals and cause problems for recreation and navigation on
waterbodies that it infests.
Zebra mussel
(Dreissena polymorpha)
First Identified in US: 1988
Native Range: Eurasia
U.S. Distribution: All of the Great Lakes and many
associated tributaries, plus other states throughout the U.S.
Description: Sticky strands secreted from one side of shell.
Can grow very thick on surfaces.
Impacts: Documented to grow very thick on surfaces, foul
marine engines, clog intake pipes, wash up in windrows on
beaches, and alter the aquatic food web by reducing the
amount of algae in the water due to high filter-feeding rates.
Photos credits: Hydrilla, Amy P. Smagula, NH DES. Zebra mussels, NH SeaGrant.
18
National Lakes Assessment A Collaborative Survey of the Nation's Lakes
-------
CHAPTER 3.
THE BIOLOGICAL CONDITION
OF THE NATION'S LAKES
IN THIS CHAPTER
^ Lake Health - The Biological Condition of Lakes
^ Stressors to Lake Biota
^ Ranking of Stressors
-------
Chapter 3 The Biological Condition of the Nation's Lakes
Chapter 3
The Biological Condition
of the Nation's Lakes
The Clean Water Act explicitly aims "to
restore and maintain the chemical, physical
and biological integrity of the nation's waters".
Although the NLA report does not include
all aspects of biological integrity or review
all possible chemical, physical or biological
stressors known to affect water quality, it
does pres"ent the results of some important
indicators for estimating the condition of the
nation's lakes and characterizing the key
influences.
This and the following two chapters
describe the results of the NLA using three
approaches to assess lake condition. The
first approach evaluates whether lakes are
able to support healthy aquatic plant and
animal communities. Analysts evaluated key
stressors to lake biota, such as chemical and
physical habitat attributes, and ranked the
stressors in order of importance. Second, the
recreational suitability of lakes was assessed
and the risk of exposure to algal toxins was
evaluated (Chapter 4). Finally, the third
approach was to evaluate trophic state based
on chlorophyll-a levels (Chapter 5).
Lake Health -
The Biological Condition of Lakes
The biology of a lake is characterized in
terms of the presence, number, and diversity
of fish, insects, algae, plants and other
organisms that together provide accurate
information about the health and productivity
of the lake ecosystem. The number and
kinds of plant and animal species present in a
lake system are a direct measure of a lake's
overall well-being.
The NLA includes information from two
biological communities or assemblages -
phytoplankton and zooplankton in its
evaluation of lake condition. The primary
basis for assessing biological health in the
NLA is an index of taxa loss which is applied
to the phytoplankton and zooplankton data.
The NLA uses planktonic O/E taxa loss as
the predominant measure of overall lake
condition because it is based on both plant
and animal data and thus will reflect a
broader perspective of trends in lakes. A
second approach is also presented using
an index of biotic integrity that is applied
to sediment diatoms, a distinct type of
phytoplankton. Both models use the biological
reference conditions developed from the set
of reference lakes (see Chapter 2).
Phytoplankton and Zooplankton
Phytoplankton are microscopic plants
(algae) that float in the water and are
usually responsible for both the color and
clarity of lakes. Because of their ability to
photosynthesize, they are a primary source
-------
Chapter 3
The Biological Condition of the Nation's Lakes
of energy in most lake systems, providing the
food source for higher order organisms such
as zooplankton or small fishes. Phytoplankton
are remarkably diverse. For example, certain
phytoplankton can regulate the depth at
which they reside, optimizing their ability to
access both nutrients and light. Others are
specific to certain habitats within lakes, and
to certain nutrient and chemical conditions.
^
->
'//,
Centrate (left) and pinnate (right) diatoms. Image? courtesy
of J bmol a-j provided by D c h.tr (<,
Zooplankton are small free-floating
aquatic animals. The zooplankton community
constitutes an important element of the
aquatic food chain. These organisms serve
as an intermediary species in the food chain,
transferring energy from planktonic algae
(primary producers) to larger invertebrate
predators and fish. Both phytoplankton and
zooplankton are highly sensitive to changes
in the lake ecosystem. The effects of
environmental disturbances can be detected
through changes in species composition,
abundance, and body size distribution of
these organisms.
Diatoms
Diatoms are a group of algae. Typically
abundant in marine and freshwater habitats,
diatoms account for at least 20% of the
primary production on earth (i.e., they use
the sun's energy to turn carbon dioxide and
water into food and energy). Unique among
the algae, diatoms have cell walls composed
of silica (glass), which are intricate and
beautiful as well as useful for identifying
individual species. In lakes, diatoms grow
suspended in water as well as attached to
substrates. Biologists use the diatoms in the
water column and those on the lake bottom
as a reflection of conditions in the lake water
column. When diatoms die, they settle to
the bottom and the silica shell remains intact.
Over time their silica shells are preserved in
layer upon layer of lake sediments enabling
researchers to look at conditions that existed
in the past. Similar to other biological
indicators, diatoms integrate the physical
and chemical conditions of the lake and
surrounding watershed in which they reside.
The environmental conditions under which
particular diatom species flourish vary greatly
and have been well-described, making them a
useful indicator.
Index of Taxa Loss -
The Observed/Expected (O/E) Ratio
NLA analysts used the planktonic O/E
taxa loss model to assess the condition of
the planktonic community combining data
from both phytoplankton and zooplankton.
The O/E measure looks at whether or not
-------
Chapter 3
The Biological Condition of the Nation's Lakes
organisms (taxa) one would expect to find,
based on reference lakes, are in fact present.
The model allows a precise matching of the
taxa found in the sample in this case
phytoplankton and zooplankton taxa with
those that should occur under the specified
natural environmental conditions defined
by the reference sites. The list of expected
taxa (or"E") at individual sites are predicted
from a model developed from data collected
at reference sites. By comparing the list
of taxa observed (or "0") at a site with
those expected to occur, one can quantify
the proportion of taxa that have been lost
presumably due to stressors present in
the lake. The 0/E model is widely used
nationally and internationally to assess the
condition of aquatic communities. The index
is particularly attractive because it allows a
direct comparison of conditions across the
different types of aquatic systems (e.g.,
lakes, wetlands, streams, and estuaries)
that will be assessed by the national aquatic
resource surveys.
Typically 0/E values are interpreted
as the percentage of the expected taxa
present. Each tenth of a point less than 1
represents a 10% loss of taxa at the site;
thus, an 0/E score of 0.9 indicates that 90%
of the expected taxa are present and 10%
are missing. The higher the percentage, the
healthier the lake. As with all indicators,
0/E values must be interpreted in context
of the quality of reference sites because the
quality of reference sites available in a region
sets the bar for what taxa may be expected.
Regions with lower-quality reference sites
may have fewer taxa or different taxa and
thus will have a lower bar. Although an O/E
value of 0.8 means the same thing regardless
of a region, i.e., 20% of taxa have been
lost relative to reference conditions in each
region, the true amount of taxa loss will be
under-estimated if reference sites are of
lower quality, meaning more disturbed than
reference sites in comparable regions.
For the phytoplankton and zooplankton
data, NLA analysts developed three
regionally-specific O/E models to predict the
extent of taxa loss across lakes of the United
States. They defined three categories of
plankton taxa loss: good (<20% taxa loss),
fair (20-40% taxa loss), and poor (>40%
taxa loss).
Index of Biological Integrity -
The Lake Diatom Condition Index
The Lake Diatom Condition Index
(LDCI) or the Diatom IBI is similar in
concept to an economic indicator (e.g., the
Consumer Confidence Index) in that the
total index score is the sum of scores for a
variety of individual measures. To calculate
economic indicators, economists look at a
number of metrics, including new orders for
consumer goods, building permits, money
supply, and others that reflect economic
growth. To determine the LDCI, ecologists
looked at taxonomic richness, habit and
trophic composition, sensitivity to human
disturbance, and other aspects of the
assemblage that are reflective of a natural
state. For the LDCI, NLA analysts calculated
regionally-specific thresholds that were based
on percentages of reference lake distributions
of LDCI values.
-------
Chapter 3 The Biological Condition of the Nation's Lakes
The development of the LDCI is a
groundbreaking addition to the tools available
to perform lake assessments. The metrics
used to develop the LDCI for the NLA covered
five characteristics of diatom assemblages
that are routinely used to evaluate biological
condition:
Taxonomic richness: This characteristic
represents the number of distinct taxa, or
groups of organisms, identified within a
sample. A greater number of different kinds
of taxa, particularly those that belong to
pollution-sensitive groups, indicate a variety
of physical habitats and an environment
exposed to generally lower levels of stress.
Taxonomic composition: Ecologists
calculate composition metrics by identifying
the different taxa groups, determining which
taxa in the sample are ecologically important,
and comparing the relative abundance of
organisms in those taxa to the whole sample.
Healthy (good quality) lake systems have
diatoms from across a larger number of taxa
groups, whereas stressed (poor quality) lakes
are often dominated by a high abundance of
organisms in a small number of taxa that are
tolerant of pollution.
Taxonomic diversity: Diversity metrics look
at all the taxa groups and the distribution
of organisms among those groups. Healthy
lakes should have a high level of diversity of
diatoms present.
Morphology: Organisms are characterized
by certain adaptations, including how they
move and where they live. These habits
are captured in morphological metrics. For
example, some are designed to move freely
up and down within the water column to
maximize nutrient uptake or light exposure,
while others may develop adaptations, such
as coloration, to avoid predation. A diversity
of such attributes is reflective of a lake
that naturally includes a diversity of habitat
niches.
Pollution tolerance: Each taxa can tolerate
a specific range of chemical contamination,
which is referred to as their pollution
tolerance. Once this range is exceeded, the
taxa are no longer present. Highly sensitive
taxa, or those with a low pollution tolerance,
are found only in lakes with good water
quality.
Findings of the Biological Assessments
Using the planktonic 0/E, or taxa loss
model, 56% of the nation's lakes are in good
condition, while 21% are in fair condition, and
22% are in poor condition (Figure 6). The
LDCI shows similar results with 47% of lakes
in good condition, 27% in fair condition, and
23% in poor condition. For the continental
U.S., this means about half of the country's
lakes are in good condition, while the other
half are experiencing some level of stress that
is negatively affecting the aquatic biological
communities.
-------
Chapter 3
The Biological Condition of the Nation's Lakes
Natural lakes in general exhibit slightly
lower overall plankton taxa loss than man-
made lakes. Sixty-seven percent of natural
lakes are in good condition as compared to
40% of man-made lakes. The LDCI indicates
that the proportion of lakes exhibiting good
conditions does not vary significantly between
natural and man-made lakes. However, 30%
of natural lakes as compared to 13% of man-
made lakes exhibit poor biological condition
based on the diatom LDCI.
Although in many cases the results
of the planktonic 0/E analysis are similar
to the results of the LDCI analysis, such
agreement will not always occur. The taxa
loss index examines a specific aspect of
biological condition (biodiversity loss) and
the index of biological integrity analysis
combines multiple characteristics to evaluate
biological condition. In this instance, the two
' , rj
, -- LV
Planktonic O/E
Diatom IBI
558%
665%
Natural
(29,308)
Man-Made
(20,238)
47 1%
44.8%
503%
communities may be responding differently
to the stresses impacting lakes or to different
stresses.
Stressors to Lake Biota
In the aquatic environment, a stressor
can be anything (chemical, biological or
physical) that has the potential to impact its
inhabitants by altering their surroundings
outside their normal ecological range. There
are many external occurrences that can alter
a creature's ability to thrive, both natural
and otherwise. Drought or rapid draw-down
can be a stressor; an invading species can
be a stressor; and human activity can be
a stressor. An important dimension of the
national lakes assessment is to evaluate key
chemical and physical stressors of lake quality
that, when altered, have the potential to
impact lake biota.
Number
of Lakes
23.317
13.353
11.490
13.134
6.904
8.824
10.184
6.448
2.665
1. Chemical Stressors
For this report, five key
chemical indicators of lake
stress were evaluated. These
are total phosphorus
concentration, total nitrogen
concentration, turbidity, acid
neutralizing capacity (ANC),
and dissolved oxygen
concentration (DO).
0 20 40 60 80 100
Percentage of Lakes
<= 20% = Good
I 1 20 - 40% = Fa*
>40%-Poor
0 20 40 60 80 100
Percentage of Lakes
^m Good
r1 Fair
Poor
Figure 6. Assesment of quality
using the Planktonic O/E Taxa
Loss and Lake Diatom Condition
Index for lakes nationwide and
for natural vs.man-made lakes.2
For this and all figures in this report, values for good, fair and poor may not add to one hundred percent. Lakes sites that were not assessed and
indicators for which no value was recorded are not included. Please refer to the Technical Report for further discussion on the statistical significance
of these two terms and how they were evaluated.
-------
Chapter 3
The Biological Condition of the Nation's Lakes
Phosphorus, Nitrogen,
and Turbidity
Findings for Nutrients
and Turbidity
Phosphorus and nitrogen are critical
nutrients required for all life. In appropriate
quantities, these nutrients support the
primary algal production necessary to support
lake food webs. In many lakes, phosphorus
is considered the "limiting nutrient,"
meaning that the available quantity of this
nutrient controls the pace at which algae
are produced in lakes. This also means that
modest increases in available phosphorus can
cause very rapid increases in algal growth
(measured as chlorophyll-a). Some lakes are
limited by nitrogen. In these lakes, modest
increases in available nitrogen will yield
the same effects. When excess nutrients
from human activities enter lakes, cultural
eutrophication is often the result. The
culturally-accelerated eutrophication of lakes
has a negative impact on everything from
species diversity to lake aesthetics.
Turbidity is a measure of light scattering;
more specifically, murkiness or lack of
clarity. Lakes that are characterized by high
concentrations of suspended soil particles
and/or high levels of algal cells will
have high measured turbidity. Turbidity
in lakes is natural in some instances,
resulting from natural soil deposition and
resuspension within the lakes themselves.
When human activities in lake watersheds
and riparian zones increase soil erosion,
increased turbidity often results in
smothering of nearshore habitats by
sediments and/or changing algae growth
patterns. These changes affect biological
and recreational conditions.
Phosphorus, nitrogen, and turbidity are
linked indicators that jointly influence both
the clarity of water and the concentrations of
algae that are measured in a lake. The levels
of these three indicators vary regionally,
as do the relationships between nutrients
and turbidity, and between nutrients and
chlorophyll-a. For phosphorus, nitrogen, and
turbidity, lakes were assessed in relation to
regionally-specific thresholds based on the
distributions in a distinct set of reference
lakes (see Chapter 2).
Survey results show that slightly over half
of the nation's lakes are in good condition
with respect to phosphorus and nitrogen
(Figure 7). Fifty-eight percent and 54% of
lakes are not stressed for the two nutrients,
respectively. Conversely, 42% of lakes are in
fair or poor condition for phosphorus levels
and 46% are in fair or poor condition for
nitrogen. For both nutrients, there are no
significant differences between natural lakes
and man-made lakes.
Turbidity
Man-Made
(20,238)
Figure 7. Phosphorus, nitrogen, and
turbidrty in three lake classes.
Natural
(29,308)
0 20 40 60 80 100 0 204060801000 20 40 60 80 100
Percentage of Lakes
^H Good I I Fax Poor
National Lakes Assessment; A Collaborative Survey of the Nation's Lakes
-------
Chapter 3 The Biological Condition of the Nation's Lakes
For turbidity, 78% of lakes are in good
condition, 16% are in fair condition, and 6%
are in poor condition. When comparing the
natural lakes to the man-made lakes for this
indicator, 75% of natural lakes are in good
condition as compared to 81% of man-made
lakes.
Lake Acidification
While not a widespread problem, lake
acidification continues to be an important
indicator of lake condition in a small number
of spots around the country. Acid rain and
acid mine drainage are major sources of
acidifying compounds and can change the
pH of lake water, impacting fish and other
aquatic life. Acid neutralizing capacity
(ANC) serves as an indicator for sensitivity
to changes in pH. The ANC of a lake is
determined by the soil and underlying
geology of the surrounding watershed. Lakes
with high levels of dissolved bicarbonate
ions (e.g. limestone watersheds) are able
to neutralize acid depositions and buffer the
effects of acid rain. Conversely, watersheds
that are rich in granites and sandstones and
contain fewer acid-neutralizing ions have
low ANC and therefore a predisposition to
acidification.
ANC Assessment Thresholds
Non-acidic
Acidic-natural
Anthropogenically
acidified
>50
< 50
and
peq ANC
Meq. ANC
DOC < 5
mg/L
<0 meg ANC and
DOC < 5 mg/L
Maintaining stable and sufficient ANC is
important for fish and aquatic life because
ANC protects or buffers against drastic
pH changes in the waterbody. Most living
organisms, especially aquatic life, function at
the optimal pH range of 6.5 to 8.5. Sufficient
ANC in surface waters will buffer acid rain
National
(49,546)
Natural
(29,308)
Man-Made
(20,238)
10%
0%
08%
0%
14%
0%
510
0
29.073
235
0
19963
275
0
0 20 40 60 80 100
Percentage of Lakes
Non-Acidic I 1 Acidic-Natural
I Acidic-Human Caused
Figure 8. Acid Nuetralizing Capacity for lakes of the U.S.
and prevent pH levels to stray outside this
range. In naturally acidic lakes, the ANC may
be quite low, but the presence of natural
organic compounds in the form of dissolved
organic carbon, or DOC, can mitigate the
effects of pH fluctuations.
Findings for Lake Acidification
Results from the NLA indicate that almost
all, or 99%, of the nation's lakes can be
classified as in good condition with respect
to ANC (Figure 8). When looking at these
results, however, it is also important to note
that although the NLA indicates that lake
acidification is not a widespread problem,
acidification on a smaller scale, i.e., "hot
spots," do occur. While only a relatively
small proportion of lakes may be impacted
by acidification, the effects of acidification in
the impacted lakes, and the contribution of
acidity to other stressors, can be severe in
specific geographic regions.
National Lokes Assessment A Collaborc
-------
Chapter 3
The Biological Condition of the Notion's Lakes
Dissolved Oxygen
Dissolved oxygen, or DO, is considered
one of the more important measurements
of water quality and is a direct indicator of a
lake's ability to support aquatic life. Aquatic
organisms have different DO requirements for
optimal growth and reproduction. Decreases
in DO can occur during winter or summer
when the available dissolved oxygen is
consumed by aquatic plants, animals, and
bacteria during respiration. While each
organism has its own DO tolerance range,
generally levels below 3 mg/L are of concern.
Conditions below 1 mg/L are referred to as
hypoxic and are often devoid of life.
Findings for Dissolved Oxygen
For the NLA, DO assessment thresholds
were established as high (> 5 mg/L),
moderate (>3 to <5), and low (<3 mg/L),
and were based on measurements from
the top two meters in the middle of the
lake (Figure 9). Eighty-eight percent of the
country's lakes display high levels of DO and
are in good condition (Figure 9). Natural
lakes perform slightly better than the nation
as a whole with 94% in good condition. Man-
made lakes results show 80% with high levels
of DO.
These findings provide insights that low
DO is not a chronic problem near the lake
surface, which was not surprising given the
sampling approach used in the survey. Future
surveys may be able to more adequately
address DO conditions in the bottom waters
of lakes where low DO conditions are more
likely to occur first.
2. Physical Habitat Stressors
Lakes are highly interactive systems.
The physical and chemical make-up of a lake
supports a specialized community of biological
Natural
(29,308)
Man-Made
(20,238)
0 20 40 60 80 100
Percentage of Lakes
High (> 5 mgl/Li c 1 Moderate I > 3 mg/L)
^m Low (<- 3 mg/L) I 1 No Data
Figure 9. Dissolved oxygen for lakes of the U.S.
organisms unique to the surrounding
environment. Lakes and ponds are still-water
habitats that host a large array of floating
organisms that cannot survive in flowing
water. Shoreline and shallow water habitats
provide refuge for many organisms from
predation, living and egg-laying substrates,
and food. Due to the distinct habitat of
lakes, many creatures have developed special
features for an aquatic or semi-aquatic
lifestyle. Frogs and other amphibians, for
example, lay their eggs in the water. Here
the juveniles will grow and only as they
mature, venture onto land. Emergent plants
along the lake's edges (irises, arrowheads
and cattails), floating plants (water lilies),
free-floating leaved plants (duckweed and
bladderwort), submerged plants (milfoil
and pondweed), and algae (phytoplankton
and diatoms) provide food, shelter,
protection, and nesting places for the lake's
invertebrates, amphibians, fish, and aquatic
mammals. In addition to aquatic inhabitants,
a wide number of terrestrial animals rely on
-------
Chapter3 The Biological Condition oft/ie Nation's Lakes
Figure 10. Schematic of a lakeshore
lakes for their food. For example, in a typical
summer, a moose can eat over 171/? Ibs of
aquatic plants per day. A 3Vz Ib adult osprey
can consume some 270 Ibs of fish in one year.
The condition of lakeshore habitats (Figure
10) provides important information relevant
to lake biological health. The indicators
include the vegetation and physical features
along shorelines and adjacent upland areas,
and the aquatic plants living in the near
shore shallows including the natural features
(snags, rock outcrops, etc). Shoreline
structure affects nutrient cycling, biological
production, and even sedimentation rates
within the lake. The zone of transition
between the lakeshore and the water's edge
is an area where considerable biological
interactions occur and is critically important
to benthic communities, fish, and other
aquatic organisms. The relationship between
the terrestrial and aquatic environments is
characterized by the movement of nutrients/
food from the shore to the water (e.g., fish
making use of emergent plants for food or
shelter), and the reverse movement from
the water back to the shore (e.g., seasonal
flooding of shorelines, shore birds feeding on
aquatic insects and crustaceans). Therefore,
the physical habitat condition of the land-
water interface is critically important to
overall lake condition.
-------
Chapter 3 The Biological Condition of the Nation's Lakes
Human activities along lakeshores often
adversely affect these ecosystem functions
by lessening the amount and type of optimal
habitat available. Habitat cover or protection,
in the form of woody snags, overhanging
trees, and aquatic plants, becomes markedly
reduced. A poor habitat cover adversely
impacts macrophytes, fish, and other living
things in and around the lake. Alterations of
these and other types of habitat features can
affect biological integrity even in lakes where
the water is not polluted.
For the NLA, physical habitat condition
was assessed based on observations for four
indicators: 1) lakeshore habitat, 2) shallow
water habitat, 3) physical habitat complexity
(an index of habitat at the land-water
interface), and 4) human disturbance (extent
and intensity of human activity). In assessing
the physical habitat complexity indicator,
NLA analysts looked at not only the total
amount of cover present but also the diverse
types of cover and the complex nature of
potential ecological niches. For each lake
habitat indicator, values were compared to
the distribution of the indicator value in the
reference sites.
Habitat Stressors
The lakeshore habitat indicator examines
the amount and type of shoreline vegetation.
It is based on observations of three layers
of coverage (understory grasses and forbs,
mid-story non-woody and woody shrubs, and
overstory trees). In general, lakeshores are
in better condition when shoreline vegetation
cover is high in all three layers. It is important
to note, however, that not all three layers
naturally occur in all areas of the country. For
example, in the northern plains areas, there
is typically no natural overstory tree cover.
Similarly, in some areas of the intermountain
west, steep rocky shores are the norm for
high-mountain and/or canyon lakes. These
natural features have been factored into the
calculation of the lakeshore habitat indicator.
The shallow water habitat indicator
examines the quality of the shallow edge of
the lake by utilizing data on the presence
of living and non-living features such as
overhanging vegetation, aquatic plants
(macrophytes), large woody snags, brush,
boulders, and rock ledges. Lakes with greater
and more varied shallow water habitat are
typically able to more effectively support
aquatic life because they have more, and
more complex, ecological niches. Like the
lakeshore habitat indicator, the shallow water
indicator is related to conditions in reference
lakes and is modified regionally to account for
differing expectations of natural condition.
The third indicator, physical habitat
complexity, combines data on from the
lakeshore and shallow water interface. This
indicator estimates the amount and variety
of all cover types at the water's edge. Like
the other indicators, this index is related
to conditions in reference lakes and is
modified regionally to account for differing
expectations of natural condition.
-------
Chapter 3
The Biological Condition of the Notion's Lakes
Findings for Habitat Stressors
The findings for the three habitat stressor
indicators are depicted in Figures 11, 12
andlB. Nationally, 46% of lakes exhibit
good lakeshore habitat condition, while
18% of lakes are in fair condition and 36%
are in poor condition. With respect to the
shallow water areas of lakes, 59% of lakes
exhibit good habitat condition, while 21% of
indicators, more natural lakes support healthy
combined habitat condition than man-made
lakes.
Lakeshore Human Disturbance
In the above discussion of the lakeshore
environment, the condition of lakes was
described in terms of habitat integrity in both
the lakeshore and shallow water areas of the
National
(49,546)
Natural
(29,308)
Man-Made
(20,238)
Number
Lakeshore Habitat of Lakes
359%
45.5%
50.4%
32 6%
384%
40.8%
22.546
8.832
17.807
14.775
4.843
9.547
7.771
3.989
8.260
0 20 40 60 80 100
Percentage of Lakes
Good I I Fair Poor
Figure 11. Lakeshore habitat for lakes of the U.S. as percent of
lakes in three condition classes.
National
(49,546)
Natural
(29,308)
Man-Made
(20,238)
Shallow Water Habitat
0 20 40 60 80 100
Percentage of Lakes
Good
Fair
I Poor
Figure 12. Shallow water habitat for lakes of the U.S.
as percent of lakes in three condition classes.
lakes are in fair condition, and 20% are in
the most disturbed, or poor condition. For
physical habitat complexity of the land/water
interface, 47% of lakes are in good condition,
20% of lakes are in fair condition, and 32%
are in poor condition. For all three habitat
lake. The fourth indicator of physical habitat
is lakeshore human disturbance and reflects
direct human alteration of the lakeshore
itself. These disturbances can range from
minor changes (such as the removal of trees
to develop a picnic area) to major alterations
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 3
The Biological Condition of the Nation's Lakes
(such as the construction of a large lakeshore
residential complex complete with concrete
retaining walls and artificial beaches). The
effects of lakeshore development on the quality
of lakes include excess sedimentation, loss of
native plant growth, alteration of native plant
communities, loss of habitat structure, and
modifications to substrate types. These impacts,
in turn, can negatively affect fish, wildlife, and
other aquatic communities.
(Figure 14). In contrast to the other three
habitat indicators, the percentage of natural
lakes that have low lakeshore disturbance is
substantially higher than that of man-made
lakes. Forty-six percent of natural lakes are
in good condition compared to 18% of man-
made lakes. These findings also show that
there are twice as many man-made lakes with
high lakeshore disturbance (poor condition) as
natural lakes.
National
(49,546)
Natural
(29,308)
Man-Made
(20,238)
Physical Habitat
Complexity
0 20 40 60 80 100
Percentage of Lakes
National
(49,546)
Natural
(29,308)
Man-Made
(20,238)
Lakeshore Disturbance
348%
I- H 47 6%
464%
I 1 41.3%
I 1 56 9%
24 1%
17.259
23.600
8364
13.586
12.091
3.490
3.673
11.509
4,874
I Good
I Fair
Poor
0 20 40 60 80 100
Percentage of Lakes
Good I I Fair Hi Poor
Figure 13. Physical habitat complexity for the lakes of the
U.S. as percent of lakes in three condition classes.
Findings for Lakeshore Disturbance
Across the lower 48 states, 35% of lakes
exhibit good conditions representative of
relatively low human disturbance levels, while
48% of lakes exhibit moderate disturbance, and
17% exhibit poor, or highly disturbed conditions
Figure 14. Lakeshore disturbance for lakes of the U.S. as
percent of lakes in three conditions classes.
-------
Chapter 3 The Biological Condition of the Nation's Lakes
Lakeshore Alteration Stress
By Kellie Merrell, VT Department of Conservation
Transformation of lakeshores from natural forested and wetland cover to lawns and sandy beaches,
accompanied by residential homes development (and redevelopment) is a stressor to many lakes. In a survey
of 345 lakes in the Northeast during the early 1990s, the U.S. Environmental Protection Agency and U.S. Fish
and Wildlife Service determined that the stress from shoreline alteration was a more widespread problem
than eutrophication and acidification. In recent years, many state agencies have documented the effects of
shoreline development on nearshore and shallow water habitat quality with notable results.
As lakeshores are converted from forests to lawn, impervious surfaces, and sand, enhanced runoff results
in increased embeddedness, less shading, and in most cases, more abundant aquatic plant growth in
the shallows. Shallow water habitat is further simplified bythe direct removal of woody structure, and
interruption in the resupply of this critical habitat component. The Wisconsin Department of Natural
Resources has estimated that unbuffered developed sites contribute five times more runoff, seven times
more phosphorus and 18 times more sediment to a lake than the naturally forested sites.
This alteration of the nearshore and shallow water habitat affects a variety of both terrestrial and aquatic
wildlife and has been described in the literature. Green frog, dragonfly, and damselfly populations decline.
The nesting success and diversity of fish species also declines, with sensitive native species being replaced
by more disturbance tolerant species. Turtles lose basking sites and corridors to inland nest sites. Bird
composition shifts from insect-eating to seed-eating species. Even white-tailed deer are affected, with
reduction in winter browse along shorelines reducing winter carrying capacity. The removal of conifers along
shores also reduces shoreline mink activity. Ultimately, the cumulative effects of lakeshore development have
negative implications for many species of fish and wildlife.
Ranking of Stressors
An important key function of the national
assessments is to provide a perspective on key
stressors impacting biological condition in lakes
and rank them in terms of the benefits expected
to be derived from reducing or eliminating these
stresses. For the NLA, analysts used three
approaches to rank stressors. The first looks
at how extensive or widespread any particular
stressor is, e.g., how many lakes have excess
phosphorus concentrations. The second
examines the severity of the impact from an
individual stressor when it is present, e.g., how
severe is the biological impact when excess
phosphorus levels occur. Ranking ultimately
requires taking both of these perspectives into
consideration. Finally the third approach is
attributable risk, which is a value derived by
combining the first two risk values into a single
number for ranking across lakes.
Throughout this section, the stressors are
assessed and reported independently and as
such do not sum to 100%. Most lakes are likely
to experience multiple stressors simultaneously
which can result in cumulative effects rather
than those elicited by a single stressor.
Relative Extent
Relative extent in the NLA is simply a way
of evaluating how widespread and common a
particular stressor is among lakes. Stressors
that occur over a small area (i.e., hotspots)
or that occur over a wide area but are sparse
have a low relative extent. It is important for
water resource mangers to take into account
the extent of the stressor when setting priority
actions at the national, regional, and state
scale.
National Lakes Assessment; A Collaborative Survey of the Nation's Lakes
-------
Chapter 3 The Biological Condition of the Nation's Lakes
Nationally,
the most
widespread
stressors
measured as part
of the NLA are
those that affect
the shoreline and
shallow water
areas, which in
turn can affect
biological condition. Results from the NLA
show that the most widespread of these is the
alteration of lakeshore habitat.
Thirty-six percent of lakes nationally
have poor lakeshore habitat (Figure 15 - left
graph). The second most prevalent stressor is
the physical habitat complexity, which is poor
in 32% of lakes nationally. Total nitrogen
and total phosphorus ranked fourth and fifth,
respectively, in terms of how widespread
excess levels are across the country.
The ranking of these stressors according
to extent is similar across natural and
man-made lakes with most stressors being
more widespread in man-made lakes (e.g.,
lakeshores with poor habitats occurring at
41% of man-made lakes compared with 33%
of natural lakes).
Relative Risk
The evaluation of relative risk is a way
to examine the severity of the impact of
a stressor when it occurs. Relative risk
is used frequently in the human health
field. For example, a person who smokes
is 10-20 times more likely to get and die of
lung cancer3. Similarly, one can examine
the likelihood of having poor biological
conditions when phosphorus concentrations
are high compared with the likelihood of
poor biological conditions when phosphorus
concentrations are low. When these two
3Center of Disease Control, http:// www.cdc.gov/cancer/luna/risk tactors.htm
likelihoods are quantified, their ratio is called
the relative risk. For the NLA, only the
relative risk of stressor to poor conditions is
presented.
Results of the relative risk analyses for
NLA are presented in the middle graph of
Figure 15. The highest relative risk nationally
was found for lakeshore habitat disturbance
with a relative risk just over 3. This means
that lakes with poor surrounding vegetation
are about 3 times more likely to also have
poor biological conditions, as defined for
this assessment. The remaining stressors,
with the exception of dissolved oxygen and
lakeshore disturbance, have relative risks
near 2 (i.e., twice as likely to have poor
biological conditions). The relative risks for
stressors in natural lakes appear consistently
greater than the relative risk values for man-
made lakes.
Attributable Risk
As mentioned, attributable risk is
derived by combining the relative extent
and the relative risk into a single number
'y of the Nation's Lakes
-------
Chapter 3
The Biological Condition of the Nation's Lakes
for the purposes of ranking. Conceptually,
attributable risk provides an estimate of
the proportion of poor biological conditions
that could be reduced if poor conditions of a
particular stressor were eliminated. This risk
value represents the magnitude or importance
of a potential stressor and one that can be
ranked and prioritized for policy makers and
managers.
Estimates for attributable risk based on
the planktonic O/E indicator of biological
condition are presented in right graph of
Figure 15. Lakeshore habitat alteration has
the highest attributable risk for plankton taxa
loss while other stressors (with the exception
of lakeshore disturbance, turbidity and
dissolved oxygen) have similar attributable
risk values. Thus one might expect that
to improve lake condition to the greatest
extent, lakeshore vegetative habitat would
have to be increased to the point that it is
no longer a stressor. Natural lakes show a
slightly different pattern in attributable risk
with lakeshore habitat being a high priority
followed closely by total nitrogen, total
phosphorus and physical habitat complexity.
For man-made lakes, three of the four habitat
indicators rank the highest in attributable
risk.
Number Relative Risk to
Relative Extent 0/u!kes Biological Condition Attributable Risk
Lakeshore Habitat
Physical Habitat Complexity
Shallow Water Habitat
National Total Nitrogen
(49,546) Total Phosphorus
Lakeshore Disturbance
Turbidity
Dissolved Oxygen t 13%
Lakeshore Habitat
Physical Habitat Complexity
Natural Shallow Water Habitat
(29,308)
Total Nitrogen
Total Phosphorus
Lakeshore Disturbance
Turbidity
Dissolved Oxygen
Lakeshore Habitat
Physical Habitat Complexity
Man-Made ShatlowWater "*«
(20238) Total Nitrogen
Total Phosphorus
Lakeshore Disturbance
Turbidity
Dissolved Oxygen L 2.4%
17,807
16,033
9.980
9,467
9.006
8.364
3.100
632
9,547
8.366
5.025
5,690
4.955
3.490
1.148
153
8.260
7.667
4.954
3.777
4.051
4.874
1.952
480
0 20 40 60 80 100
80 20 40 60 80 100
Figure 15. Relative Extent of Poor Stressors Conditions Nationally and in Natural and Man-Made Lakes,
Relative Risks of Impact to Plankton O/E and Attributing Risk (combining Relative Extent and Relative Risk).
-------
CHAPTER 4.
SUITABILITY FOR RECREATION
Algal Toxins
Contaminants in Fish Tissue
Pathogen Indicators
-------
Chapter 4 Suitability for Recreation
Chapter 4
Suitability for Recreation
Another perspective on lake condition
views lake quality in terms of its suitability
or safety for recreational use. Lakes are
used for a wide variety of recreational
opportunities that include swimming,
waterskiing, windsurfing, fishing, boating, and
many other activities. However, a number
of microbial organisms, algal toxins, and
other contaminants present in lakes can
make people sick. NLA analysts assessed
three indicators with respect to recreational
condition: 1) microcystin - one type of
algal toxin, 2) cyanobacteria - one type of
algae that often produces algal toxins, and
3) chlorophyll-a - a measure of all algae
present. Samples were collected for two
other indicators, pathogens and sediment
mercury, however results are unavailable at
this time. Results from a companion study of
contaminants in fish tissue are available and
are also discussed in this chapter.
Algal Toxins
One group of phytoplankton, the
cyanobacteria, produces a biochemically and
bioactively diverse number of toxins, called
cyanotoxins. Cyanobacteria (also called
blue-green algae) are a natural part of all
freshwater ecosystems. Eutrophication often
results in conditions that favor their growth
and cyanobacterial blooms frequently occur in
these types of lakes. Cyanobacterial blooms
can be unsightly, often floating in a layer of
decaying, odiferous, gelatinous scum. Many
types of cyanobacteria have the potential to
producing cyanotoxins, including Anabaena,
Microcystis, and Oscillatoria/Planktothrix,
and several different cyanotoxins may be
produced simultaneously. In assessing
the risk of exposure to algal toxins for
recreational safety, it is important to
remember that algal density i.e., chlorophyll-a
concentrations and cyanobacteria cell counts
serve as proxies for the actual presence
of algal toxins. This is because not all
phytoplankton are cyanobacteria and not all
cyanobacteria produce cyanotoxins.
-------
Although there are relatively few
documented cases of severe human health
effects, exposure to cyanobacteria or their
toxins may produce allergic reactions such
as skin rashes, eye irritations and respiratory
symptoms and in some cases gastroenteritis,
liver and kidney failure, or death. The most
likely exposure route for humans is through
accidental ingestion or inhalation during
recreational activities, though cyanotoxins
Chapter 4 Suitability for Recreation
cyanotoxin, or any other algal toxins, the
World Health Organization (WHO) has
established recreational exposure guidelines
for chlorophyll-a, cyanobacterial cell counts,
and microcystin (Table 1).
These thresholds, along with the presence
or absence of microcystin, were used to
assess the condition of lakes of the nation
with respect to this indicator suite.
Indicator (units)
Chlorophyll-a
(M9/L)
Cyanobacteria
cell counts
(#/L)
Microcystin
(M9/L)
Low Risk
<10
< 20,000
<10
Moderate Risk
10 - <50
20,000 - <100,000
10 - <20
High Risk
>50
> 100,000
>20
Table 1. World Health Organization thresholds of risk associated with potential exposure to cyanotoxins.
are also cause for concern in drinking water.
Cyanotoxins can also kill livestock and
pets that drink affected water. While many
varieties of cyanotoxin exist, microcystin,
produced by several cyanobacterial taxa, is
currently believed to be the most common in
lakes. Microcystin is a potent liver toxin, a
known tumor promoter, and a possible human
carcinogen.
Because of the potential for human
illness, several states have issued guidelines
for recreational use advisories associated with
the presence of microcystin or associated
indicators. These guidelines vary and rely on
visual observations of algal scums, measured
chlorophyll-a concentrations, cyanobacteria
cell counts, and/or direct measurements of
microcystin. While EPA does not presently
have water quality criteria for microcystin,
Findings for Algal Toxins
Using the WHO thresholds, the levels of
risk associated with the exposure to algal
toxins varied by region and by indicator
(Figure 16). Using the cyanobacteria
cell count as the indicator, 27% of lakes
nationwide pose a high or moderate risk for
potential exposure to algal toxins. There was
no significant difference in the proportion of
natural and man-made lakes with high or
moderate exposure risks for cyanobacteria.
The potential high or moderate exposure
risk to algal toxins based on chlorophyll-a
concentration or microcystin levels is 41%.
It is important to note, however, that
while the risk of exposure is extremely
low, microcystin was present in 30% of
lakes nationally (Figure 17). This could
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 4 Suitability for Recreation
Chlorophyll-a
National
(49,546)
Natural
(29,308)
Man-Made
(20,238)
Cyanobacteria Microcystin Risk
0.7%
02%
11.3%
03%
0%
0%
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100
Percentage of Lakes
Low Risk I 1 Moderate Risk OB High Risk
Figure 16. Percent of lakes in three algal toxin risk categories, using three different indicators.
potentially have wide ranging impacts on
human health and the swimmability of many
lakes. When interpreting the data of this
first ever national-scale study of microcystin
in lakes, it is necessary to consider how the
sampling was conducted. During the 2007
survey, microcystin samples were collected
at mid-lake, in open water. However, large
windblown accumulations of cyanobacteria
often occur at nearshore areas in lakes and
it is the concentrations along the lake's
edge that are of most concern to municipal
health officials. Some studies indicate that
cell counts and cyanotoxin concentrations
are greater in nearshore scums than in open
water areas. However, while concentrations
are often greater in nearshore accumulations
than in open water areas, concentrations
large enough to cause human health concerns
may still occur in open waters (with or
without surface accumulations or scums).
Sampling at mid-lake provides a conservative
estimate and because of
this, the NLA results may
underestimate certain
types of recreational
exposure when
accumulations or scums
are present.
Another important
point to consider when
looking at the data
is whether the single
sample of microcystin
truly represents what is
in the lake. Chlorophyll-a
levels, cyanobacteria
densities, and cyanotoxin
concentrations may
change quite rapidly,
depending on bloom
intensity and weather
conditions. The
concentrations of
microcystin measured
on one particular day
may over or underestimate season-wide
central tendencies. The NLA is not intended
to assess the specific condition of any given
lake, but rather provide information on the
general conditions across the population of
lakes. Finally, it is currently unknown how
well microcystin occurrence correlates with
the occurrence of other classes of cyanotoxins
that were not measured, or how human
health risks might be altered because of toxin
mixtures. While the survey results are a good
start in our understanding, much more is to
be learned about algal toxins in lakes.
Contaminants in Lake Fish Tissue
Fish acquire contaminants and
concentrate them in their tissues by uptake
from water (bioconcentration) and through
ingestion (bioaccumulation). Fish can
often bioaccumulate chemicals at levels of
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 4 Suitability for Recreation
National
(49,546)
Natural
(29,308)
Man-Made
(20,238)
Microcystin
Presence
Number
of Lakes
30.1%
( 30.6%
I 29.5%
14.929
8.955
5.975
0 20 40 60 80 100
Percentage of Lakes
Figure 17. Occurrence of microcystin in lakes.
more than a million times the concentration
detected in the water column. In a review
of existing studies and programs, a need
emerged for a comprehensive characterization
of chemical contamination in freshwater fish
tissue and identification of the extent of that
contamination in U.S. lakes and reservoirs.
In a study conducted by the Office of
Water's Office of Science and Technology, EPA
surveyed contaminants in lake fish tissue.
The National Study of Chemical Residues in
Lake Fish Tissue characterized contaminant
levels in fillet tissue for predators and in
whole bodies for bottom-dwelling fish species.
The study targeted pollutants that were
classified as persistent, bioaccumulative, and
toxic (PBT) chemicals, including mercury,
arsenic, PCBs, dioxins and furans, DDT,
and chlordane. This survey provided data
to develop national estimates for 268 PBT
chemicals in fish tissue from lakes and
reservoirs in the 48 continental states
(excluding the Great Lakes and the Great Salt
Lake).
The study focused on fish species that
are commonly consumed in the study area,
have a wide geographic distribution, and
potentially accumulate high concentrations of
PBT chemicals. Fish samples were collected
over a 4-year period (2000-2003) from 500
randomly selected lakes and reservoirs,
which ranged in size from 1 hectare (2.5
acres) to 365,000 hectares (900,000 acres),
were at least 1 meter (3 feet) deep, and had
permanent fish populations.
-------
Chapter 4 SuitoMity for Recreation
Contaminants in Predator Fish
The data show that mercury, PCBs,
dioxins and furans, and DDT are widely
distributed in lakes and reservoirs across
the country. Mercury and PCBs were
detected in all fish samples (Figure 18).
Dioxins and furans were detected in 81%
of the predator samples and 99% of the
bottom-dwelling fish samples. DDT was
detected in 78% of the predator samples
and 98% of the bottom-dwelling samples.
Cumulative frequency distribution
plots showed that established human
consumption limits were exceeded in 49%
of the sampled lakes for mercury, in 17%
of the lakes for total PCBs, and in 8%
of the lakes for dioxins and furans. In
contrast, 43 targeted chemicals were not
detected in any sample. Full results from
this study can be found at http://www.epa.
gov/waterscience/fishstudy.
Pathogen Indicators
Enterococci are bacteria that live in
the intestinal tracts of warm-blooded
creatures, including humans. They are
most frequently found in soil, vegetation,
and surface water because of contamination
by animal excrement. Most species of
enterococci are not considered harmful
to humans however the presence of
enterococci in the environment indicates
the possibility that other disease-causing
agents also carried by fecal material may be
present. Epidemiological studies of marine
and freshwater beaches have established
a relationship between the density of
Enterococci in the water and the occurrence
of gastroenteritis in swimmers. Enterococci
are believed to provide a better indication of
the presence of pathogens than fecal coliform,
which is an older indicator of potential
pathogenicity.
For the NLA, enterococci were measured
using a method to assess ambient
Mercury
PCBs
80
100
Figure 18. Percentage predator fish with mercury and PCB levels
above and below EPA recommend limits.
concentrations. This Quantitative Polymerase
Chain Reaction (qPCR) method quantifies
DNA that is specific to enterococci. Published
epidemiological studies report a clear
relationship between levels of qPCR-measured
enterococci and sickness. EPA research is still
underway to develop health-based thresholds
for interpreting qPCR results.
-------
V
HIGHLIGHT
Atmospheric Contaminants:
Mercury and Acid Rain
Neil C. Kamman
Vermont Department of Environmental Conservation
Of the many stressors that affect lakes, atmospheric contaminants are perhaps the most difficult to
address. This is because sources of atmospheric contaminants are often hundreds or even thousands
of miles from the lakes into which the contaminants are ultimately deposited. The intertwined issues of
freshwater acidification and mercury contamination are not new. The popular press began reporting on
acid rain in the 1970s. It took another 10-15 years for the press to also focus on mercury. Today, many
people are aware of both issues, yet often do not fully comprehend nor appreciate the degree to which the
two are linked. In this section, the sources, fate, and transport of mercury and acid-forming chemicals are
outlined to provide an understanding of where these contaminants occur, how they are manifested, and
how they are related. In the case of both these pollutants, the cycle is initiated by emissions into the air.
Mercury is a naturally occurring metal that is found in the environment in many forms, all of which are
toxic to aquatic life in varying degrees. The release of mercury to the environment is enhanced by human
activities such as the combustion of fossil fuels (such as coal and petroleum). In the U.S. the largest
sources of mercury are coal-fired generation or utility boilers, followed by waste incinerators. Mercury is
present in many household items, notably thermostats and fluorescent lamps, and is released when these
items end up in landfills or incineration facilities. Depending on its chemical form, air-borne mercury may
remain in the atmosphere for a period of minutes (as reactive gaseous mercury), days (as particulate
mercury), or weeks or years (as gaseous elemental mercury).
Methylmercury, one of the most toxic forms of mercury, can be prevalent in fish and has documented
adverse health effects on humans. The U.S. Centers for Disease Control and Prevention estimates that
up to 6% of women of childbearing age have blood mercury levels in excess of established safety levels.
Fish and fish-eating wildlife such as the common loon and American bald eagle are also at risk from
mercury toxicity. While the mercury cycle in lakes is quite complex, there are five basic stages: emission,
deposition, methylation*, bioaccumulation, and finally sequestration to lake sediments.
Lake acidification is most commonly caused by acidic deposition (rain, snow and dust). The acidic
deposition pathway begins with the release into the air of acid-forming chemicals, most notoriously sulfur
dioxide and nitrogen oxides, and ends when sulfuric and nitric acids are deposited to the landscape. Sulfur
dioxide, like mercury, results largely from the burning of fossil fuels. Some forms of coal are very rich in
sulfur, and poorly controlled facilities released massive quantities, particularly during the period 1960-
1992. Both sulfur dioxide and nitrogen oxides are common components of vehicular emissions. Once
emitted, these two compounds undergo complex atmospheric transformations, resulting in rain and snow
that contain dilute concentrations of nitric and sulfuric acids. Thankfully, the Clean Air Act Amendments of
1990 have resulted in profound reductions in acid-forming precursors. In very sensitive regions, however,
lakes remain at risk for acidification even with reduced levels of acid rain.
In one sense, the process of lake acidification is not as complex as that of mercury accumulation in
that there is neither methylation nor bioaccumulation of the acids. Yet acidification has more pernicious
effects that can exacerbate mercury problems. Acidification of watersheds renders the watersheds more
efficient at creating and transporting methylmercury to lakes, along with other soil-bound toxic metals
such as aluminium. Moreover, acidification of the lakes themselves renders the bioaccumulation of
'The natural and biologically-mediated process by which mercury is transformed into toxic organic methylmercury.
National Lakes Assessment A Collaborative Survey of the Nation's Lakes
41
-------
methylmercury more efficient. Therefore, acidic lakes: 1) receive more mercury from their watershed, 2)
have more of the mercury in the toxic methylated form, and 3) have more efficient bioaccumulation of the
methylmercury.
Studies throughout the United States, Canada, Russia, and Scandinavia all show a very strong
connection between lake acidification and mercury bioaccumulation. Researchers have documented the
occurrence of mercury hotspots in various parts of the U.S. and attribute these to one of three basic
causes proximity to poorly-controlled emissions sources, water level management in reservoirs, or acid
sensitive landscapes. In regions of North America where lake acidification is in fact already improving,
minor reductions in mercury in fish and fish-eating wildlife can be anticipated. Much more consequential
reductions in environmental mercury contamination are expected as EPA and states strive to control
mercury emissions from coal-fired utilities and other sources.
Mercury enters a lake by:
- Direct deposition
Flow through wetlands
»- Subsurface flow through soils
- Runoff through streams
% Methyl 50%
mercLry
Meth>1 merr.ury Water PhytoplanHon 2ooplar*ton Pl»m-«ating fish
btoacomjtation
lictor
Graphical depiction of methylmercury bioaccumulation in lake biota. This figure is reproduced from the
Hubbard Brook Research Foundation's ScienceLinks publication Mercury Matters: Linking Mercury
Science with Public Policy in the Northeastern United States. Used with permission.
42
National Lakes Assessment A Collaborative Survey of the Nation's Lakes
-------
CHAPTER 5.
TROPHIC STATE OF LAKES
r
IN THIS CHAPTER
Findings for Trophic State
-------
Chapter 5 Trophic Stote of Lakes
Chapter 5
Trophic State of Lakes
The third approach to assessing the
condition of lakes is to look at lakes with
respect to their primary production. Trophic
state depicts biological productivity in lakes,
especially primary productivity. Lakes with
high nutrient levels, high plant production
rates, and an abundance of plant life are
termed eutrophic, whereas lakes that have
low concentrations of nutrients, low rates
of productivity and generally low biomass
are termed oligotrophic. Lakes that fall in
between are mesotrophic, and those on
the extreme ends of the scale are termed
hypereutrophic or ultra-oligotrophic. Lakes
exist across all trophic categories, however
hypereutrophic lakes are usually the result
of excessive human activity and can be an
indicator of stress conditions.
There is no ideal trophic state for lakes
as a whole since lakes naturally fall in
all of these categories. Additionally, the
determination of "ideal" trophic state depends
on how the lake is used or managed. For
example, for drinking water purposes an
oligotrophic lake is a better source than a
eutrophic lake because the water is easier
or less expensive to treat. Swimmers and
recreational users also prefer oligotrophic
lakes because of their clarity and aesthetic
quality. Eutrophic lakes can be biologically
diverse with abundant fish, plants, and
wildlife. For anglers, increased concentrations
of nutrients, algae, or aquatic plant life
generally result in higher fish production.
Eutrophication
is a slow, natural
part of lake
aging, but today
human influences
are significantly
increasing the
amount of
nutrients entering
lakes. Human
activities such as
poorly managed
agriculture or
suburbanization
of lakeshores
can result in
excessive nutrient concentrations reaching
lakes. This can lead to accelerated
eutrophication and related undesirable effects
including nuisance algae, excessive plant
growth, murky water, odor, and fish kills.
-------
Chapter 5 Trophic State of Lakes
Findings for Trophic State
For the NLA, trophic state of lakes is
characterized using nationally-consistent
chlorophyll-a concentrations (Figure 19).
Based on these thresholds, 13% of lakes are
oligotrophic, 37% are mesotrophic, 30% are
eutrophic, and 20% are hypereutrophic. The
results also show that natural lakes tend
towards mesotrophic conditions and man-
made lakes towards eutrophic conditions.
Many states and lake associations classify
their lakes by trophic state using a variety
of thresholds for nutrients (phosphorus
or nitrogen), Secchi disk transparency,
or chlorophyll-a, depending on the data
available. For this assessment, NLA analysts,
in consultation with a number of state
and local lake experts, decided to base
trophic state on chlorophyll-a. The group
considered this indicator the most relevant
and straightforward estimate of trophic state
because it is based on direct measurements
of live organisms, yet acknowledges that
other indicators also could be used. Table 2
illustrates the percentages that would fall into
the different trophic categories if different
indicators were used. Total nitrogen and total
phosphorus, (which ranked fourth and fifth
in terms of how widespread excess levels are
across the country) together or individually
are primary drivers of eutrophication.
National
(49,546)
Natural
(29,308)
Man-Made
(20,238)
Trophic State
Chlorophyll
Number
of Lakes
0 20 40 60 80 100
Percentage of Lakes
^B Oligotrophic (<= 2 ug/L)
Mesotrophic (>2-7 ug/L j
Ml Eutrophic (>7 to 30 mg/LI
1H Hypereutrophic (> 30 ug/L)
Figure 19. Trophic state of lakes in the U.S.
Table 2. Percent of U.S. lakes (natural and man-made) by trophic state, based on four alternative trophic state indicators. *
Indicator
Chlorophyll-a
Secchi
transparency
Total Nitrogen
Total Phosphorus
Oligo-trophic
12.8
10.5
22.1
25.0
Meso-trophic
36.6
22.5
37.5
28.8
Eutrophic
30.1
39.8
22.0
24.7
Hyper-eutrophic
20
18.4
18.4
21.4
' Rows may not sum to 100% due to unassessed lakes.
National Lakes Assessment: A Collaborative Surrey of the Nation's Lak
-------
HIGHLIGHT
Volunteer Power:
Monitoring Lakes with Volunteers
Hundreds of organizations monitor lakes in the U.S. using trained volunteers. Some volunteer groups
are run by state environmental agencies. Others are managed by local residential lake associations
determined to protect the quality of their local lake, pond or reservoir. Universities, often as part of
U.S. Department of Agriculture Cooperative Extension, manage a number of statewide lake volunteer
monitoring programs. In some states, trained volunteers are the leading source of consistent, long-
term lake data. Volunteer-collected lake data are widely used in state water quality assessment reports,
identification of impaired waters, local decision making, and scientific study.
One national program designed to promote the use of volunteers in
lake monitoring is the Secchi Dip-In (http://dipin.kent.edu/index.htm).
Run by limnologist Dr. Robert Carlson of Kent State University. Since
1994, the Dip-In encourages individuals who are members of a volunteer
monitoring program to measure lake transparency at or around the
4th of July and report their results on a national website. These values
are used to assess the transparency of volunteer-monitored waters in
the U.S. and Canada. One goal of the Dip-In is to increase the number
and interest of volunteers in environmental monitoring and to provide
national level recognition of the work that they perform.
Volunteer Monitoring and the National Lakes Assessment
The relationship between lake volunteer monitoring and the National Lakes Assessment (NLA) is in
its earliest stages. However, volunteers did participate in a few states where links between volunteer
programs and state monitoring staff were strong. The Vermont Department of Environmental Conservation
(DEC) conducted it's own statistically valid assessment of 50 lakes
including NLA-selected lakes about half of which are also routinely
sampled by volunteers in the DEC-managed Vermont Lay Monitoring
Program. Volunteers were informed ahead of time when NLA sampling
crews were going to arrive, and in some cases were able to provide
boats for the crews as well as welcome local advice regarding lake
navigation and access. In Rhode Island, some volunteers conducted
side-by-side sampling with the NLA crews for later analysis and
comparison using Rhode Island Watershed Watch methods. Volunteers
observed the sampling, assisted crews with equipment, provided
firsthand knowledge of local lakes, and contacted news media to provide
publicity. In Michigan, at two lakes also monitored by Michigan's Cooperative Lake Monitoring Program,
volunteers sampled side-by-side with Michigan Department of Environmental Quality staff and NLA survey
crews. Local newspaper reporters observed these monitoring events and provided press coverage of the
volunteers working alongside the survey crews.
Volunteer monitors are important partners in the assessment and protection of the nation's lakes, and
state agencies and EPA should continue to explore pathways for improved communication and cooperation
with volunteer programs in future surveys of the nation's lakes.
46
National Lakes Assessment A Collaborative Survey of the Nation's Lakes
-------
CHAPTER 6.
ECOREGIONAL RESULTS
Nationwide
Comparisons
Northern
Appalachians
Southern
Appalachians
Upper Midwest
Temperate Plains
Southern Plains
Northern Plains
Western Mountains
Xeric
-------
Chapter 6 Ecoregional Results
Chapter 6
Ecoregional Results
Taken individually, each lake is a reflection
of its watershed. The characteristics of the
watershed, i.e., its size relative to the lake,
topography, geology, soil type, land cover,
and human activities, together influence the
amount and nature of material entering the
lake. For example, a deep alpine lake located
in a Rocky Mountain watershed will likely
have clear, pristine water and little biological
productivity. Conversely, a lake in a coastal
plains watershed of the mid-Atlantic region,
an area of nutrient-rich alluvial soils and a
long history of human settlement, will more
likely be characterized by high turbidity,
high concentrations of nutrients and organic
matter, prevalent algal blooms, and
abundant aquatic weeds and other plants.
Atmospheric deposition of airborne pollutants,
as well as nutrients traveling in groundwater
from hundreds of miles away, can affect the
watershed and influence the lake condition.
Lakes in high population areas are
especially vulnerable. Combined sewer
overflow and stormwater runoff can carry
marked amounts of pollutants, such as
metals, excess sediment, bacteria, and
most recently, Pharmaceuticals. As a result,
expectations and lake condition vary across
the country.
Because of this diversity in landscape,
it becomes important to assess waterbodies
in their own geographical setting and the
NLA was designed to report findings on an
ecoregional scale. Ecoregions are areas that
contain similar environmental characteristics
and are defined by common natural
characteristics such as climate, vegetation,
soil type, and geology. By looking at lake
conditions in these smaller ecoregions,
decision makers can begin to understand
patterns based on landform and geography
- in other words, whether the problems are
isolated in one or two adjacent regions, or
whether they are widespread.
NLA Analytn Regans'
rup CJ SPL
I I SAP t~ 1 NPL
CPl LJ XER
GQ TPL HVAIT
Figure 20. Ecoregions used as part of the National Lakes Assessment.
-------
Chapter 6 Ecoregionol Results
EPA has defined ecoregions at various
scales, ranging from coarse ecoregions at the
continental scale (Level I) to finer ecoregions
that divide the land into smaller untis (Level
III or IV). The nine NLA ecoregions are
aggregations of the Level III ecoregions
delineated by EPA for the continental U.S.
These nine ecoregions as shown in
Figure 20 are:
Northern Appalachians (NAP)
Southern Appalachians (SAP)
Coastal Plains (CPL)
Upper Midwest (UMW)
Temperate Plains (TPL)
Southern Plains (SPL)
Northern Plains (NPL)
Western Mountains (WMT)
Xeric (XER)
To assess waters within each ecoregion,
the NLA captures the geographic variation
in lakes using regionally-
specific reference
conditions. The resulting
set of reference lakes
all share common
characteristics and
occur within a common
geographic area.4 This
approach not only allows
lakes in one region to
be compared with the
particular reference lakes
of that region, but also
allows for the comparison
of one ecoregion to
another. This means that
lakes in the arid west are
not being assessed against
lakes in the Southern
Plains. At the same time,
this also means that if
10% of the Xeric west
lakes were in poor condition and 20% of the
southern plains lakes were relatively poor, one
can compare the two ecoregions and say that
the Southern Plains have twice the proportion
of lakes in poor condition.
Nationwide Comparisons
Biological Condition - Taxa Loss
Regionally, the proportion of lakes with
good biological condition ranges from 91% in
the Upper Midwest to < 5% in the Northern
Plains (Figure 21). In general, the glaciated
and/or mountainous regions have the highest
proportion of lakes exhibiting good biological
condition, followed by Coastal Plains lakes.
The Xeric west and Northern Plains exhibit the
highest proportions of lakes in poor condition
biologically. Forty nine percent of lakes are in
poor biological condition in the Xeric region,
while just under 85% of Northern Plains lakes
are in poor biological condition.
Biological Quality - Planktonic O/E
<= 20% Taxa Loss
|> 40% Taxa Loss
H 20-40% Taxa Loss
Figure 21. Biological condition of the nation's lakes across nine ecoregions based on planktonic O/E taxa loss.
4. It is important to note that the geographic boundaries of trie regionally-specific reference areas do not specifically match those of the nine ecoregions.
More detailed information about how regional reference lakes were determined can be found in the Technical Report.
-------
Chapter 6 Ecoregional Results
Lakeshore Habitat
Figure 22. Habitat
condition of the
nation's lakes across
nine ecoregions
based on lakeshore
habitat.
Poor
Habitat Stressors -
Lakeshore Habitat
In the NLA, habitat stress was assessed
using four indicators: lakeshore habitat,
shallow water habitat, physical habitat
complexity and human disturbance. Of
these, the most revealing indicator, based on
the relative and attributable risk analyses,
is lakeshore habitat. This analysis indicates
that biological integrity of lakes is three times
more likely to be poor when the lakeshore
habitat area is classified as poor. Regionally,
the proportion of lakes with poor lakeshore
habitat ranges from a low of 25% in the
Northern Appalachians to a high of 84% in the
Northern Plains (Figure 22). High proportions
of poor lakeshore habitat are most prevalent
in the Plains and Xeric ecoregions.
Trophic Status
Regionally, the proportion of lakes
classified as oligotrophic, based on measures
of chlorophyll-a, ranges from 54% in the
Western Mountains to < 5% in the Temperate
Plains (Figure 23). The highest proportions of
mesotrophic waters are found in the Northern
and Southern Appalachians, and the Upper
Midwest. The proportion of eutrophic lakes is
highest in the Coastal and Southern Plains.
Hypereutrophic lakes are most prevalent in
the Temperate Plains, where nearly 50% of
lakes are classified hypereutrophic.
Recreational Suitability -
Cyanobacteria (blue-green algae)
Regionally, the proportion of lakes
presenting low risk of human exposure to
cyanobacteria-derived toxins (< 20,000
cells/L) exceeds 75% in the Western
Mountains, Xeric west, Upper Midwest, and
Northern and Southern Appalachians. The
highest proportions of lakes at high risk
(> 100,000 cells/L) occur in the Southern,
Coastal, and Temperate Plains. The Northern
Plains have over 50% of lakes in the
moderate risk category (Figure 24).
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 6 Ecoregional Results
Trophic Condition - Chlorophyll
Figure 23. Trophic state of
the nation's lakes across
nine ecoregions based on
chlorophyll-a.
| Oligotrophic | j Mesotrophic | Eutrophic ^| Hypereutrophic
Recreational Conditions - Cyanobacteria
Figure 24. Comparison of
recreational risk of the nation's
lakes across nine ecoregions,
based on blue-green algae
levels corresponding to World
Health Organization risk levels.
I Low Risk n Moderate Risk Hiah Risk
-------
Chapter 6 Ecoregiono) Results
Northern Appalachians
The Landscape
The Northern Appalachians ecoregion
covers all of the New England states, most of
New York, the northern half of Pennsylvania,
and northeast Ohio. It encompasses New
York's Adirondack and Catskill Mountains and
Pennsylvania's mid-northern tier, including the
Allegheny National Forest. Major waterbodies
include Lakes Ontario and Erie, New York's
Finger Lakes, and Lake Champlain. There are
5,226 lakes in the Northern Appalachians that
are represented by the NLA, 54% of which
are constructed reservoirs. The ecoregion
comprises some 139,424 square miles (4.6%
of the United States), with about 4,722
square miles (3.4%) under federal ownership.
Based on satellite images in the National Land
Cover Dataset (1992), the distribution of
land cover is 69% forested and 17% planted/
cultivated, with the remaining 14% of land in
other types of cover.
Many lakes in the region were created
for the purpose of powering sawmills. During
the 18th and early 19th centuries, lakes were
affected by sedimentation caused by logging,
farming, and damming of waterways. When
agriculture moved west and much of eastern
farmland converted back into woodlands,
sediment yields declined in some areas. In
many instances, lakes in what appears to
be pristine forested settings are in fact still
recovering from prior land use disturbances.
In the mountainous regions of the Northern
Appalachian ecoregion, many large reservoirs
were constructed throughout the early 20th
century for the purpose of hydropower
generation and/or flood control.
Findings
A total of 93 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
the ecoregion. An overview of the NLA
findings for Northern Appalachian lakes is
shown in Figure 25.
Biological Condition
Fifty-five percent of lakes are in good
biological condition based on planktonic
O/E, and when using the diatom IBI, 67% of
lakes in the ecoregion are in good biological
condition relative to reference condition.
Conversely, the percentages of lakes in poor
condition are 15% and 10% based on the two
analyses, respectively.
Trophic Status
Based on chlorophyll-a, 26% of lakes
are oligotrophic, 54% are mesotrophic, 17%
are eutrophic, and only 3% are considered
hypereutrophic.
Recreational Suitability
Using the indicators and World Health
Organization guidelines described in Chapter
3, most lakes in the Northern Appalachian
ecoregion exhibit relatively low risk of
exposure to cyanobacteria and associated
cyanotoxins. Based on cyanobacterial counts,
95% of lakes exhibit low risk. Microcystin
was present in 9% of lakes.
Physical Habitat Stressors
Lakeshore habitat is considered good in
66% of the lakes in this ecoregion. However,
given the long history of land use and
settlement in this ecoregion, the shorelines of
Northern Appalachian lakes exhibit relatively
disturbed conditions due to human activities.
Fifty-seven percent of lakes show moderate to
high levels of lakeshore disturbance.
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 6 Ecoregionol Results
Northern Appalachians
5,226 Lakes
0 20 40 60 80 100 0 20 40 60 80 100 0 20 4O 60 80 100 0 20 40 60 80 100
Percentage of Lakes Percentage of Lakes Percentage of Lakes Percentage of Lakes
For Lake Origin: ^ Low Risk * Abwm "jWGood Hi Good
Natural 9>M Man-Made I I Moderate Risk Present L__J Fair CZ3 Fair
For Plankton O/E
i^B < 20% Taxa Lou
> 40% Taxa Lou
High Risk
I 20-40% Taxa Loss
Poor
I Poor
Figure 25. NLA results for the Northern Appalachian Plateau Ecoregion. Bars show the percentage of lakes within
a condition class for a given indicator.
Chemical Stressors
In contrast to physical habitat conditions,
the majority of Northern Appalachian lakes
exhibit high-quality waters based on the NLA
stressor indicators. Relative to regionally-
specific reference expectations, total
phosphorus and nitrogen, chlorophyll-a, and
turbidity levels are considered good in 80%
or more of lakes in this ecoregion. Lakes are
in good condition based on ANC and DO when
compared to nationally-consistent thresholds.
Southern Appalachians
The Landscape
The Southern Appalachian Plateau
ecoregion stretches over 10 states,
from northeastern Alabama to central
Pennsylvania. Also included in this region are
the interior highlands of the Ozark Plateau
and the Ouachita Mountains in Arkansas,
Missouri, and Oklahoma. The region covers
about 321,900 square miles (10.7% of the
United States) with about 42,210 square
miles (10.7%) under federal ownership.
Many important public lands, such as the
Great Smoky Mountains National Park and
surrounding national forests, the Delaware
Water Gap National Recreation Area,
the George Washington and Monongahela
National Forests, and the Shenandoah
National Park are located within the region.
Topography is mostly hills and low mountains
with some wide valleys and irregular plains.
Piedmont areas are included within the
Southern Appalachians ecoregion.
Natural lakes are nearly non-existent
in this ecoregion. The 4,690 lakes in the
Southern Appalachian ecoregion represented
by the NLA are all man-made. The
-------
Chapter 6 Ecoregiono) Results
V/-<-r
'S?**
Southern Appalachians
4.690 Lakes
Lake Origin
Diatom IBI
830%
Trophic State - Chlorophyll
112*
-Uses
H186*
-|256%
0 20 40 80 80 100 0 20 40 60 80 100 0 20 40 60 80
Percentage of Lakes Percentage of Lakes Percentage of Lakes
Present Good
ForLake Origin
^m Natural ajijj Man-Made
For Plankton O/E
< 20% Taxa Loss
> 40% Taxa Loss
For Diatom IBI:
^m Good I 1 Fair
Poor
For Trophic State - Chlorophyll
jV Oligotrophc <<= 2 ug/L) I
VI Eutrophic (>7 to 30 mg/L) I
Low Risk
I Moderate Risk
I High Risk
I Absent
Fair
Poor
20-40% Taxa Loss
I Mesotrophic (>2-7 ug/L)
I Hypereutrophic (> 30 ug/L)
tOO 0 20 40 60 80 100
Percentage of Lakes
^m Good ^m Good
Fair I I Fair
Poor ^H Poor
Not Assessed
Figure 26. NLA results for the Southern Appalachian Ecoregion. Bars show the percentage of lakes within a condition class for a given indicator.
configuration of the Southern Appalachian
valleys has proven ideal for the construction
of man-made lakes, and some of the nation's
largest hydro-power developments can be
found in the Tennessee Valley.
Findings
A total of 116 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
the ecoregion. An overview of the NLA
findings for the Southern Appalachian lakes is
shown in Figure 26.
Biological Condition
Forty-two percent of lakes are in good
biological condition based on planktonic
O/E and when using the diatom IBI, 63% of
lakes in the ecoregion are in good biological
condition relative to reference condition.
Conversely, the percentages of lakes in poor
condition are 31% and 13% based on the two
analyses, respectively The apparent difference
between these two biological indices goes
beyond the scope of this assessment but
may suggest that the two indicators are
responding to different stressors in lakes in
this particular ecoregion.
-------
Chapter 6 Ecoregional Resu/ts
Trophic Status
Based on chlorophyll-a, 12% of lakes
are oligotrophic, 46% are mesotrophic,
17% are eutrophic, and 26% are considered
hypereutrophic.
Recreational Suitability
While many lakes in the Southern
Appalachian ecoregion exhibit relatively
low risk of exposure to cyanobacteria and
associated cyanotoxins, a large portion of
lakes exhibit moderate risk levels. When
looking at the cyanobacterial counts, 73%
of lakes exhibited low risk. Microcystin was
present in 25% of lakes.
Physical Habitat Stressors
Lakeshore habitat is considered good
in 42% of the lakes in this ecoregion. Yet
the shorelines of Southern Appalachian
Plateau lakes indicate considerable lakeshore
development pressure. Over 90% of lakes
show moderate to high levels of lakeshore
disturbance.
Chemical Stressors
Based on the NLA stressor indicators,
a considerable proportion of Southern
Appalachian lakes exhibit good quality waters
Total phosphorus and nitrogen are considered
good in 66% and 68% of lakes, respectively.
Relative to regionally-specific reference
expectations, chlorophyll-a and turbidity
levels are considered good in 72% or more of
the man-made lakes in this ecoregion. The
man-made lakes are in good condition based
on ANC and DO when compared to nationally
consistent thresholds, although 9% of lakes
were ranked poor due to low dissolved
oxygen.
Coastal Plains
The Landscape
The Coastal Plains ecoregion covers the
Mississippi Delta and Gulf Coast, north along
the Mississippi River to the Ohio River, all
of Florida, eastern Texas, and the Atlantic
seaboard from Florida to New Jersey. Total
area is about 395,000 square miles (13% of
the United States) with 25,890 square miles
(6.6%) under federal ownership. Based on
satellite images in the 1992 National Land
Cover Dataset, the distribution of land cover
is 39% forested, 30% planted/cultivated,
and 16% wetlands, with the remaining 15%
of land in other types of cover. Damming,
impounding, and channelization in this
ecoregion have altered the rate and timing of
water flow and delivery to lakes.
A subset of major lakes of the region
includes the Toledo Bend (TX) and
Sam Rayburn Reservoirs (TX/LA), Lake
Okeechobee (FL), Lake Marion (SC), and
the massive lake-wetland complexes north
of the Gulf Coast. The Coastal Plains is also
home to a variety of lakes and ponds, such
as Cape Cod kettleholes, New Jersey Pine
Barren ponds, southeastern blackwater lakes,
Carolina "Bays", and the limestone-rich clear
lakes of the Florida peninsula. A total of 7,009
lakes and reservoirs in the Coastal Plains
ecoregion are represented in the NLA, and
69% of these are man-made.
-------
Chapter 6 Ecoregionof Results
Findings
A total of 102 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
the ecoregion. An overview of the NLA
findings for the Coastal Plains lakes is shown
in Figure 27.
Biological Condition
Forty-seven percent of lakes are in good
biological condition based on planktonic
O/E, and when using the diatom IBI, 57% of
lakes in the ecoregion are in good biological
condition relative to reference condition.
Conversely, the percentages of lakes in poor
condition are 27% and 6% based on the two
analyses, respectively
Trophic Status
Based on chlorophyll-a, 6% are
mesotrophic, 60% are eutrophic, and 34%
are considered hypereutrophic.
Recreational Chlorophyll Risk
115*
Trophic Stale - Chlorophyll
55%
^^~^^~ 00.0%
0 20 40 80 80 100 0 20406080100
Percentage of Lakes Percentage of Lakes
For Lake Origin Low Risk MB Present
NaturalHB Man-Made I I Moderate RiskflM Absent
For Plankton O/E High Risk
< 20% Taxa LossCZZl 20-40% Taxa Loss
> 40% Taxa Loss
For Diatom IB)
GoodCZZZZ] FairHH Poor
For Trophic Stale Chlorophyll
Oiigotroph.c i<= 2 ug/L) Mesotrophic (>2-7 ug/L)
Eutrophic (>7 to 30 mg/L)HB Hypereutrophic (> 30 ug/L)
0 20 40 60 80 100 0 20 40 60 80 100
Percentage of Lakes Percentage of Lakes
Good Dissolved Oxygen Habitat
Fair Good Good
Poor I"1 Fair I 1 Fair
Poor Poor
I I Not Assessed
I 1 No Data
Figure 27. NLA findings for the Coastal Plains Ecoregion. Bars show the percentage of lakes within a condition class for a given indicator.
National Lakes Asses
nent; A Collaborative Survey of (
-------
Chapter 6 Ecoregional Results
Recreational Suitability
Lakes in the Coastal Plains Ecoregion
exhibit moderate risk of exposure to
cyanobacteria and associated cyanotoxins.
Based on cyanobacterial counts, 64% of lakes
exhibited low risk. Microcystin was present in
35% of lakes.
Physical Habitat Stressors
Lakeshore habitat is considered good in
22% of the lakes in this ecoregion. Moreover,
the shorelines of the Coastal Plains lakes
are highly disturbed, indicating considerable
lakeshore development pressure in this
region. Just about 84% of lakes show
moderate to high levels of lakeshore human
disturbance.
Chemical Stressors
Based on the NLA stressor indicators,
water quality is somewhat variable across
the Coastal Plains. Total phosphorus and
nitrogen are considered good in 48% and
51% of lakes, respectively, and are poor in
15% and 4% of lakes, respectively. Relative
to regionally-specific reference expectations,
chlorophyll-a concentrations are considered
good in 65% of lakes, and turbidity levels
are considered good in 85% of lakes in this
ecoregion. Lakes are in good condition based
on ANC and DO when compared to nationally-
consistent thresholds, although 13% of lakes
were ranked fair due to low dissolved oxygen.
Upper Midwest
The Landscape
The Upper Midwest ecoregion covers
most of the northern half and southeastern
part of Minnesota, two-thirds of Wisconsin,
and almost all of Michigan, extending about
160,374 square miles (5.4% of the United
States). A total of 15,562 lakes in the
ecoregion are represented in the NLA, nearly
all of which are of natural origin, reflecting
the glaciation history of this region. Sandy
soils dominate with relatively high water
quality in lakes supporting warm and cold-
water fish communities. Major lakes of the
region include the Great Lakes (which, for
design considerations, were not represented
by the NLA), and also Lake of the Woods and
Red Lake (MN), and Lake Winnebago (WI).
The glaciated terrain of this ecoregion is
typically plains with some hill formations.
The northern tier of this ecoregion has a
very high number of smaller lakes, both
drainage and seepage, which range widely
in geochemical makeup. Much of the land
is covered by national and state forest.
Federal lands account for 15.5% of the area
at about 25,000 square miles. Based on
satellite images in the 1992 National Land
-------
Chapter 6 Ecoregional Results
Upper Midwest
15,562 Lakes
20 40
Percentage of Lakes
For Lake Origin:
^m Natural Man-Made
80 100 0
Physical Habitat Complexity
503%
40 60 80 100 0 20 40 60 80 100 0
Percentage of Lakes Percentage of Lakes
20 40 80 80 100
Percentage of Lakes
Good
CZ1 Fair
^m Poor
Low Risk ^» Present ^m Good
I Moderate Risk Absent I I Fair
For Plankton 0/E fgf High Risk Poor
^m < 20% Taxa Loss LTD 20-40% Taxa Loss
> 40% Taxa Loss
For Diatom IBI
Good I I Fair QHH Poor
For Trophic State - Chlorophyll
^m Obgotrophic (<> 2 ug.l) Mesotrophic (>2-7 ug/L)
Eutrophic <>7 to 30 mg/L) Hypereutrophic (> 30 ug/L)
Figure 28. NLA findings for the Upper Midwest ecoregion. Bars show the percentage of lakes within a condition class for a given indicator.
Cover Dataset, the distribution of land cover
is 40% forested, 34% planted/cultivated,
and 17% wetlands, with the remaining 9%
of land in other types of cover. Most of the
landscape was influenced by early logging and
agricultural activities.
Findings
A total of 148 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
the ecoregion. An overview of the NLA
findings for the Upper Midwest lakes is shown
in Figure 28.
Biological Condition
Ninety-one percent of lakes are in good
biological condition based on planktonic
0/E, and when using the diatom IBI,
47% of lakes in the ecoregion are in good
biological condition relative to reference
condition. Conversely, the percentages of
lakes in poor condition are 4% and 22%
based on the two analyses, respectively.
The apparent difference between these two
biological indices goes beyond the scope of
this assessment but may suggest that the
two indicators are responding to different
stressors in lakes in this particular ecoregion.
-------
Chapter 6 Ecoregional Results
Trophic Status
Based on chlorophyll-a, 9% are
oligotrophic, 54% are mesotrophic, 26%
are eutrophic, and 10% are considered
hypereutrophic.
Recreational Suitability
Lakes in the Upper Midwest exhibit
relatively low risk of exposure to
cyanobacteria and associated cyanotoxins.
Based on cyanobacterial counts, 81% of lakes
exhibited low risk. Microcystin was present in
23% of lakes.
Physical Habitat Stressors
Lakeshore habitat is considered good
in 54% of the lakes in this ecoregion. Yet
the shorelines of the Upper Midwest lakes,
indicate considerable lakeshore development
pressure in this region. Forty-six percent
of lakes show moderate to high levels of
lakeshore human disturbance.
Chemical Stressors
Based on the NLA stressor indicators,
water quality is relative good across the
Upper Midwest. Total phosphorus and
nitrogen are considered good in 66% and
59% of lakes, respectively, and are poor in
9% and 8%, of lakes respectively. Relative
to regionally-specific reference expectations,
chlorophyll-a concentrations are considered
good in 68% of lakes, and turbidity levels
are considered good in 77% of lakes in this
ecoregion. Lakes are in good condition based
on ANC and DO when compared to nationally-
consistent thresholds.
Temperate Plains
The Landscape
The Temperate Plains ecoregion includes
the open farmlands of Iowa; eastern North
and South Dakota; western Minnesota;
portions of Missouri, Kansas, and Nebraska;
and the flat farmlands of western Ohio,
central Indiana, Illinois, and southeastern
Wisconsin. This ecoregion covers some
342,200 square miles (11.4% of the United
States), with approximately 7,900 square
miles (2.3%) in federal ownership. The terrain
consists of smooth plains, numerous small
lakes, prairie pothole lakes, and wetlands. A
total of 6,327 lakes in the Temperate Plains
ecoregion are represented in the NLA, of
which 75% are of natural origin. Lakes of
this region are generally small, with over
60% of lakes smaller than 100 hectares in
size. Agriculture is the predominant land
use. Based on satellite images in the 1992
National Land Cover Dataset, the distribution
of land cover is 9% forested and 76%
planted/cultivated, with the remaining 15% of
land in other types of cover.
-------
Chapter 6 Ecoregional Results
Temperate Plains
6,327 Lakes
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 0
Percentage of Lakes Percentage of Lakes Percentage of Lakes
For Lake Onjin
Natural I
Man-Made
For Plankton O/E
20% Taxa Lots
> 40% Taxa Loss
For Diatom 181
Goodl~3 FarHH Poor
For Trophic State - Chtorophyt
OligotrophK (<> 2 ug/L)
Eutrophic (>7 to 30 mg'L)
Low Risk
I I Moderate R
High Risk
20-40% Taxa Loss
Present
Absent
Good
Fair
Poor
20 40 60 80 100
Percentage of Lakes
mm Good
CD Fa*
Poor
I Mesotrophic (>2-7 ug.'Li
I HypereutrophK (> 30 ug/L)
Figure 29. NLA findings for the Temperate Plains ecoregion. Bars show the percentage of lakes within a condition class for a given indicator.
Findings
Trophic Status
A total of 137 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
this ecoregion. An overview of the NLA
findings for the Temperate Plains lakes is
shown in Figure 29.
Biological Condition
One quarter, or 24%, of lakes are in
good biological condition based on planktonic
O/E, and when using the diatom IBI, 17% of
lakes in the ecoregion are in good biological
condition relative to reference condition.
Conversely, the percentages of lakes in poor
condition are 35% and 52% based on the two
analyses, respectively.
Based on chlorophyll-a, 2% are
oligotrophic, 32% are mesotrophic, 21%
are eutrophic, and 45% are considered
hypereutrophic.
Recreational Suitability
Lakes in the Temperate Plains exhibit
moderate risk of exposure to cyanobacteria
and associated cyanotoxins. Based on
cyanobacterial counts, 48% of lakes exhibited
low risk. Microcystin was present in 67%
of lakes.
-------
Chapter 6 Ecoregional Results
Physical Habitat Stressors
Lakeshore habitat is considered good
in 56% of the lakes in this ecoregion. The
shorelines of the Temperate Plains lakes
exhibit human activity disturbances, urban
development, and agricultural pressures
in this region. Sixty percent of lakes show
moderate to high levels of lakeshore human
disturbance.
Chemical Stressors
Based on the NLA stressor indicators,
water quality in the Temperate Plains is
somewhat variable. Total phosphorus and
nitrogen are considered good in 38% and
27% of lakes, respectively, and are poor in
30% and 40% of lakes, respectively. Relative
to regionally-specific reference expectations,
chlorophyll-a concentrations are considered
good in 56% of lakes, and turbidity levels
are considered good in 84% of lakes in
this ecoregion. Lakes are generally in good
condition based on ANC and DO when
compared to nationally-consistent thresholds.
However, turbidity levels are poor in 6% of
lakes, chlorophyll-a is poor in 29% of lakes,
and dissolved oxygen is fair in 12% of lakes.
Southern Plains
The Landscape
The Southern Plains ecoregion covers
approximately 405,000 square miles
(13.5% of the United States) and includes
central and northern Texas; most of western
Kansas and Oklahoma; and portions of
Nebraska, Colorado, and New Mexico. The
terrain is a mix of smooth and irregular
plains interspersed with tablelands and low
hills. Most of the great Ogallala aquifer lies
underneath this region.
Based on satellite images in the 1992
National Land Cover Dataset, the distribution
of land cover is 45% grassland, 32% planted/
cultivated, and 14% shrubland, with the
remaining 9% of land in other types of
cover. The Great Prairie grasslands, which
once covered much of the Southern Plains
region, are considered the most altered and
endangered large ecosystem in the United
States. About 90% of the original tall grass
prairie was replaced by other vegetation
or land use. Federal land ownership in the
region totals about 11,980 square miles or
approximately 3% of the total, the lowest
share of all NLA aggregate ecoregions. A
total of 3,148 lakes in the Southern Plains
ecoregion are represented in the NLA, 97%
of which are constructed reservoirs.
National Lakes Assessment: A Collaborative Survey of the Notion's Lakes
-------
Chapter 6 Ecoregiono/ Results
Trophic State - Chlorophyll
OS
IUW
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100
Percentage of Lakes Percentage of Lakes Percentage of Lakes Percentage of Lakes
For Lake Origin: Low Risk IM Present Good ^m Good
Natural Man-Made rI Moderate Risk Absent I 1 Far r~~l Fair
For Plankton O/E High Risk Poor Poor
< 20% Taxa LossCZZj 20-40% Taxa Loss
> 40% Taxa Loss
For Diatom ia
^H GoodCZ] Fa*HHi Poor
For Trophic State - Chlorophyll
^B Oligotroptiic ;<- 2 ug/L) MesotrophK (>2-7 ugiL)
I Eutrophic i>7 to 30 mg/L)HM Hypereulropnic (> 30 ug/L)
Figure 30. NLA findings for the Southern Plains ecoregion. Bars show the percentage of lakes within a condition class for a given indicator.
Findings
Trophic Status
A total of 128 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
this ecoregion. An overview of the NLA
findings for the Southern Plains lakes is
shown in Figure 30.
Based on chlorophyll-a, 9% are
oligotrophic, 14% are mesotrophic, 51%
are eutrophic, and 26% are considered
hypereutrophic.
Recreational Suitability
Biological Condition
Thirty-four percent of lakes are in good
biological condition based on planktonic
O/E, and when using the diatom IBI, 41% of
lakes in the ecoregion are in good biological
condition relative to reference condition.
Conversely, the percentages of lakes in poor
condition are 29% and 23% based on the two
analyses, respectively.
Lakes in the Southern Plains exhibit
moderate risk of exposure to cyanobacteria
and associated cyanotoxins. Based on
cyanobacterial counts, 57% of lakes exhibit
low risk. Microcystin was present in 21% of
lakes.
-------
Chapter 6 Ecoregiono/ Results
Physical Habitat Stressors
Lakeshore habitat is considered good in
37% of the lakes in this ecoregion. However,
the shorelines of Southern Plains lakes exhibit
considerable disturbed conditions due to
human activities. Ninety percent of lakes
show moderate to high levels of lakeshore
human disturbance.
Chemical Stressors
Water quality, based on the NLA stressor
indicators, is relatively good in the Southern
Plains. Total phosphorus and nitrogen
are considered good in 73% and 55% of
lakes, respectively, and are poor in 7%
and 20% of lakes, respectively. Relative to
regionally-specific reference expectations,
chlorophyll-a concentrations and turbidity
levels are considered good in >80% of lakes
in this ecoregion. Lakes are generally in
good condition based on ANC and DO when
compared to nationally-consistent thresholds.
However, dissolved oxygen is fair in 12% of
lakes.
Northern Plains
The Landscape
The Northern Plains ecoregion covers
approximately 205,084 square miles (6.8%
of the United States), including western
North and South Dakota, Montana east of the
Rocky Mountains, northeast Wyoming, and a
small section of northern Nebraska. Federal
lands account for 52,660 square miles or
a relatively large 25.7% share of the total
area. Terrain of the area is irregular plains
interspersed with tablelands and low hills.
This ecoregion is the heart of the Missouri
River system and is almost exclusively within
the Missouri River's regional watershed.
Several major reservoirs are along the
Missouri River mainstem, including Lake Oahe
and Lake Sacajawea. The total surface area
of lakes in this region is growing owing to
increased runoff coupled with flat topography.
Devil's Lake (ND) is one example, which in
1993 had a surface area of 44,000 acres and
presently covers in excess of 130,000 acres.
Based on satellite images in the 1992
National Land Cover Dataset, the distribution
of land cover is 56% grassland and 30%
planted/cultivated, with the remaining 14% of
land in other types of cover. A total of 2,660
lakes in the Northern Plains ecoregion are
represented in the NLA, 77% of which are of
natural origin.
Findings
A total of 65 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
this ecoregion. An overview of the NLA
findings for the Northern Plains ecoregion is
shown in Figure 31.
Biological Condition
One percent of lakes are in good biological
condition based on planktonic O/E, and when
using the diatom IBI, 7% of lakes in the
ecoregion are in good biological condition
relative to reference condition. Conversely,
the percentages of lakes in poor condition are
90% and 88% based on the two analyses,
respectively.
Trophic Status
Based on chlorophyll-a, 8% are
oligotrophic, 22% are mesotrophic, 48%
are eutrophic, and 22% are considered
hypereutrophic.
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 6 Ecoregionol Results
Recreational Chlorophyll Risk
323%
Northern Plains
2,660 Lakes
0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 100
Percentage of Lakes Percentage of Lakes Percentage of Lakes Percentage of Lakes
ForLake Origin BH Low Risk Present Good Good
Natural
Man-Made
1 Moderate Risk
For Plankton O(E § High Risk
< 20% Taxa I m» I - 3 20-«0% Taxa Loss
> 40% Taxa Loss
For Diatom IBI
Good
Present
Absent
Fair
Poor
Fair
Poor
Fair Poor
For Trophic State - Chlorophyll
Oligotroptiic (<= 2 ug.'L) ^M Mesotrophic (>2-7 ug/L)
Eutropnic (>7 to 30 mg/Li Hypereutrophc (> 30 ug/L)
Figure 31 . NLA findings for the Northern Plains ecoregion. Bars show the percentage of lakes within a condition class for a given indicator.
Recreational Suitability
Lakes in the Northern Plains exhibit the
highest risk of exposure to cyanobacteria
and associated cyanotoxins of all ecoregions.
Based on cyanobacterial counts, 41% of lakes
exhibit low risk. Microcystin was present in
75% of lakes.
addition to a middle and lower story. Even
taking into account the regional-specific
expectations, the NLA data show that the
Northern Plains lake shorelines exhibit very
high levels of disturbance due to human
activities. Ninety-nine percent of lakes show
moderate or high levels of lakeshore human
disturbance.
Physical Habitat Stressors
Lakeshore habitat cover is considered
good in only 7% of the lakes in this
ecoregion. Regionally-specific habitat
reference condition for the Northern Plains
is comprised of grasses and shrubs and is
different from many of the other ecoregions
where expectations include a tree layer in
Chemical Stressors
Based on the NLA stressor indicators,
water quality is variable in the Northern
Plains. In general, lakes tend to have high
levels of nutrients. Relative to regionally-
specific reference expectations, total
phosphorus concentrations are considered
poor in 71% of lakes, while total nitrogen
-------
Chapter 6 Ecoregional Results
concentrations are considered poor in 91% of
lakes. By contrast, based on chlorophyll-a,
78% of lakes are considered in good
condition, and turbidity levels are good in
70% of lakes.
In the Northern Plains ecoregion, the
conventional limnological wisdom that
biomass production is controlled simply by
nutrient concentrations may not apply. Lakes
are generally in good condition based on
ANC and DO when compared to nationally-
consistent thresholds.
Western Mountains
The Landscape
The Western Mountains ecoregion
includes the Cascade, Sierra Nevada, Pacific
Coast ranges in the coastal states; the Gila
Mountains in the southwestern states; and
the Bitterroot and Rocky Mountains in the
northern and central mountain states. This
region covers approximately 397,832 square
miles, with about 297,900 square miles or
74.8% classified as federal land the highest
proportion of federal property among the
nine aggregate ecoregions. The terrain of this
area is characterized by extensive mountains
and plateaus separated by wide valleys and
lowlands. Lakes in this region, in particular
those within smaller, high-elevation drainages
are very low in nutrients, very dilute in other
water chemistry constituents (e.g., calcium),
and therefore productivity in these systems is
limited in their natural condition. Accordingly,
these smaller, high elevation lakes are very
sensitive to effects of human disturbances
Lakes and ponds of the region range
from large mainstem impoundments to high-
mountain caldera and kettle lakes. Most
famous among these mountain caldera lakes
are Crater Lake (OR) and Lake Yellowstone
(WY). The single deepest measurement of
Secchi disk transparency made during the
NLA of 122 feet (37 meters) occurred in this
ecoregion in Waldo Lake (OR). Based on
satellite images in the 1992 National Land
Cover Dataset, the distribution of land cover
is 59% forest, 32% shrubland and grassland
with the remaining 9% of land in other types
of cover. A total of 4,122 lakes in the Western
Mountains ecoregion are represented in the
NLA, 67% of which are of natural origin.
Findings
A total of 155 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
this ecoregion. An overview of the NLA
findings for the Western Mountains lakes is
shown in Figure 32.
Biological Condition
Fifty-eight percent of lakes are in good
biological condition based on planktonic
O/E, and when using the diatom IBI, 50% of
lakes in the ecoregion are in good biological
condition relative to reference condition.
Conversely, the percentages of lakes in poor
condition are 11% and 3% based on the two
analyses, respectively.
Trophic Status
Based on chlorophyll-a, 54% of lakes
are oligotrophic, 26% are mesotrophic,
16% are eutrophic, and 4% are considered
hypereutrophic. The Western Mountains
ecoregion has the highest proportion of
oligotrophic (very clear with low productivity)
lakes of any of the ecoregions cross the
country.
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 6 Ecoregionol Results
Western Mountains
4.122 Lakes
Trophic State - Chlorophyll
54}%
K.1S
156%
42*
60
80 100 0
II 9%
117*
Physical Habitat Complexity
^^^_ SS.9S
B7S
Percentage of Lakes Percentage of Lakes
for Lake Origin: ^m Low Risk « Present
Natural Man-Made ,| Moderate Risk ^ Absenl
For Plankton O/E High Risk
< 20% Taxa in«l 1 20-40% Taxa Loss
> 40% Taxa Loss
For Diatom 181
GoodCZZ] Fair^Bi Poor
For Trophic State - Chlorophyll
^m Oligotrophic (<= 2 ug/L) ^m Mesotrophic (>2-7 ug/L)
Eutropriic (>7 to 30 mg'D Hypereutropriic (> 30 ug/L)
20 40
60
Percentage of Lakes
^m Good
I 1 Fair
Poor
80 100 0
20 40 60 80 100
Percentage of Lakes
Good
Fair
Poor
Figure 32. NLA findings for the Western Mountains ecoregion. Bars show the percentage of lakes within a condition class for a given indicator.
Recreational Suitability
Lakes in the Western Mountains exhibit
the lowest risk of exposure to cyanobacteria
and associated cyanotoxins of all ecoregions.
Based on cyanobacterial counts, 96% of lakes
exhibit low risk. Microcystin was present in
only 5% of lakes.
Physical Habitat Stressors
Lakeshore habitat is considered good in
48% of the lakes in this ecoregion. Similar
to the Northern Plains, regionally-specific
reference conditions were modified in this
ecoregion to account for sparse natural
vegetation cover types expected in this
mountainous region. With respect to human
activity along the lakeshore, this ecoregion
has the lowest percentage of lakes with
human disturbance of all regions. Forty-three
percent of lakes show moderate to high levels
of lakeshore human disturbance.
Chemical Stressors
Based on the NLA stressor indicators,
water quality in the Western Mountains is
consistently in the medium range, i.e., half
good and half bad. Relative to regionally-
specific reference expectations, total
phosphorus concentrations are considered
good in 56% of lakes, fair in 11%, and poor
in 33%. Total nitrogen concentrations are
National Lakes Assessmeni
-------
Chapter 6 Ecoregiono) Results
considered good in 52% of lakes, fair in 10%,
and poor in 38%. Based on chlorophyll-a
48% of lakes are considered in good
condition, 17% in fair condition, and 35% in
poor condition. Turbidity levels are good in
56% of lakes and fair in 31% of lakes. Lakes
are in good condition based on ANC and
DO when compared to nationally-consistent
thresholds.
Xeric
The Landscape
The Xeric ecoregion covers the largest
area of all NLA aggregate ecoregions. The
ecoregion covers portions of eleven western
states and all of Nevada for a total of about
636,583 square miles (21.2% of the United
States). Some 453,000 square miles or
71.2% of the land is classified as federal
lands, including large tracts such as the
Grand Canyon National Park (AZ), Big Bend
National Park (TX), and the Hanford Nuclear
Reservation (WA). The Xeric ecoregion is
comprised of a mix of physiographic features.
The region includes the flat to rolling
topography of the Columbia/Snake River
Plateau; the Great Basin; Death Valley; and
the canyons, cliffs, buttes, and mesas of the
Colorado Plateau. All of the non-mountainous
area of California falls in the Xeric ecoregion.
In southern areas, dry conditions and water
withdrawals produce internal drainages that
end in saline lakes or desert basins without
reaching the ocean. Large lakes in the
southwestern canyon regions are the products
of large dam construction projects. Water
levels in these lakes fluctuate widely due
to large-scale water removal for cities and
agriculture. Recently, shifts in climate and
rainfall patterns have resulted in considerably
reduced water levels on several of the major
Colorado River impoundments including Lake
Mead, Lake Powell, and Lake Havasu. Based
on satellite images in the 1992 National Land
Cover Dataset, the distribution of land cover
is 61% shrubland and 15% grassland, with
the remaining 24% of land in other types
of cover. A total of 802 lakes in the Xeric
ecoregion are represented in the NLA, 91% of
which are constructed reservoirs.
Findings
A total of 84 of the selected NLA sites
were sampled during the summer of 2007 to
characterize the condition of lakes throughout
the ecoregion. An overview of the NLA results
for the Xeric ecoregion is shown in Figure 33.
Biological Condition
Thirty-seven percent of lakes are in good
biological condition based on planktonic
0/E, and when using the diatom IBI,
70% of lakes in the ecoregion are in good
biological condition relative to reference
condition. Conversely, the percentages of
lakes in poor condition are 49% and 6%
based on the two analyses, respectively.
The apparent difference between these two
biological indices goes beyond the scope of
this assessment but may suggest that the
two indicators are responding to different
stressors in lakes in this particular ecoregion.
Trophic Status
Based on chlorophyll-a, 22% of lakes
are oligotrophic, 27% are mesotrophic,
22% are eutrophic, and 28% are considered
hypereutrophic.
Recreational Suitability
Lakes in the Xeric ecoregion exhibit low
to moderate risk of exposure to cyanobacteria
and associated cyanotoxins. Based on
cyanobacterial counts, 82% of lakes exhibit
low risk. Microcystin was present in 23% of
lakes.
National Lakes Assessment: A CoHoborawe Survey of the Nation's Lake
-------
Chapter 6 Ecoregional Results
40
60
Percentage of Lakes
Good
Fair
Poor
80 100
Percentage of Lakes
Good
Fair
Poor
0 20 40 60 80 100 0 20 40 60 80 100 0
Percentage of Lakes Percentage of Lakes
Fix Lake Origin Low Risk Present
Natural IHi Man-Made I I Moderate Risk Absent
For Plankton O/E ^" Hi8n Ri$k
< 20% Taxa Loss I 1 20-40% Taxa Loss
> 40% Taxa Loss
For Diatom IBI
Good I 1 Fair Poor
For Trophic State - Chlorophyll
Oligotrophic (<« 2 ug/L) ^B Mesotrophic (>2-7 ug L i
Eultophe <>7 to 30 mg/LJB^B Hypereulrophic (> 30 ug.'L)
Figure 33. NLA findings for the Xeric ecoregion. Bars show the percentage of lakes within a condition class for a given indicator.
Physical Habitat Stressors
Chemical Stressors
Lakeshore habitat is considered good
in 34% of the lakes in this ecoregion. In
the Xeric ecoregion, regionally-specific
reference conditions were modified to account
for sparse natural vegetation cover types
expected in this dry region. Lakes in the
Xeric ecoregion exhibit considerably disturbed
conditions due to human activities. Over
89% of lakes show moderate to high levels of
lakeshore human disturbance.
Like the Western Mountain ecoregion
to the north, the water quality in the Xeric
ecoregion is in the medium range, i.e., half
good and half bad, based on the NLA chemical
stressor indicators. Relative to regionally-
specific reference expectations, total
phosphorus concentrations are considered
good in 45% of lakes, fair in 28%, and poor
in 28%. Total nitrogen concentrations are
considered good in 40% of lakes, fair in 57%,
and poor in 3%. Based on chlorophyll-a,
50% of lakes are considered in good
condition, 21% in fair condition, and 29%
in poor condition. Turbidity levels are good
in 41% of lakes, and fair in 39%. Lakes are
good condition based on ANC and DO when
compared to nationally-consistent thresholds.
National Lakes Assessment.' A Collaborative Survey of the Nation's Lakes
-------
HIGHLIGHT
National Lake Assessment Program
Random and Reference Lake Locations
Partnerships for a Statewide Assessment
of Lake Condition
Steve Heiskary
Minnesota Pollution Control Agency
In 2007, the Minnesota Pollution Control Agency (MPCA) along
with the Minnesota Department of Natural Resources (MDNR) led
the State's participation in USEPA's National Lakes Assessment
(NLA) survey. Various other collaborators were engaged in this
study as well, including the U.S. Forest Service (USFS), the
Minnesota Department of Agriculture (MDA), and U.S. Geological
Survey (USGS). MPCA and MDNR combined on initial planning
of the survey and conducted the vast majority of the sampling.
USFS staff were instrumental in sampling of remote lakes in the
northeastern Boundary Waters Canoe Area Wilderness.
Minnesota was assigned 41 lakes as a part of the original draw
of lakes for the national survey - the most of any of the lower
48 states. The State then chose to add nine additional lakes
(randomly selected) to the survey to yield the 50 lakes needed
for statistically-based statewide estimates of lake condition. In
addition to the 50 lakes, three reference lakes were later selected
and sampled by USEPA as a part of the overall NLA effort.
As part of its statewide assessment, Minnesota opted to add several measurements of unique interest
to its overall state program. Examples of these add-ons are: pesticides, water mercury; sediment analysis
of metals, trace organics and other indicators; macrophytes species richness; fish-based lake Index of
Biotic Integrity (IBIs); and microcystin (at the index site and at a random near-shore site). A few of the
findings are highlighted here. All of the reports completed to date can be found at: http://www.pca.state.
mn.us/water/nlap.html.
Pesticides
With the exception of the corn herbicide atrazine, pesticide degradates were more frequently detected
than were the parent compounds. Possibly more of these parent compounds may have initially been
present in a greater number of lakes, but had degraded prior to sampling. Alternately, parent compounds
may have degraded early in the process, with degradates being subsequently transported to the lakes via
overland runoff. Since the peak pesticide application period is late spring to early summer, mid-summer
(July - August) lake sampling may have allowed ample time for degradation products to reach affected
lakes. MDA was a key collaborator in this effort and conducted the pesticide analysis.
Notional Lakes Assessment A Collaborative Survey of the Nation's Lakes
69
-------
Detection of Pesticides and Pesticide Degradates in Minnesota Lakes
Detection
Detection freq.
Atrazine
present
87%
Deisopropyl-
atrazine
non-detect
2%
Desethy-
atrazine
present
64%
Metolachlor
present
4%
Metolachlor
ESA
present
27%
Metolachlor
OXA
present
7%
Mercury levels
Measurement of total mercury (THg) and methyl mercury (MeHg) concentrations indicate that
high levels of THg and MeHg are distributed throughout the state. The northeastern region has higher
THg and MeHg concentrations compared to the southwestern region; although the MeHg fraction may
actually be somewhat higher in the southwestern region. Otherwise, high THg and MeHg concentrations
are distributed throughout the range of NLA lakes. These data can be used as a baseline against which to
evaluate the efficacy of mercury emissions controls in MN. The USGS was an important partner in
this effort
". i -
Aquatic Macrophytes
Plant species richness was assessed
at ten random near-shore sites on
each lake. Species richness increase
generally from south to north
peaking in the north central portion
of the State before decreasing in
the northeastern arrowhead region.
The general trend of increasing
species richness from north to
south can be explained by water
clarity, water chemistry and human
disturbance and reaffirms previous observations. The decrease in
species richness in the northeastern portion of the state can be
attributed to tannin stained waters and rocky substrate associated
with Canadian Shield lakes located throughout this region.
Continuing Partnerships
Minnesota also is collaborating on a regional assessment of lakes
in the Prairie Pothole Region with the states of North Dakota,
South Dakota, Montana and Iowa and EPA Regions V and VIII. This
collaboration will expand applications of statistically-derived data and
serve to enhance state, regional and national lake assessment efforts.
i , ' . - - . -
'. - : *. «
I*
I
70
National Lakes Assessment A Collaborative Survey of the Notion's Lakes
-------
CHAPTER 7.
CHANGES AND TRENDS
IN THIS CHAPTER
^ Subpopulation Analysis of Change -
National Eutrophication Study
^ Subpopulation Analysis -
Trends in Acidic Lakes in the Northeast
Sediment Core Analysis
-------
Chapter 7 Changes and Trends
Chapter 7
Changes and Trends
Among the long term goals of the National
Aquatic Resource Surveys is detection of
changes and trends in both the condition
of our Nation's aquatic resources and in
the stressors impacting them. Trends in
particular can be critical for policy makers to
evaluate, whether policy decisions have been
effective or whether a different approach is
necessary in order to achieve important water
quality goals.
A distinction must be made in the
type of changes and trends of interest for
development and on-going implementation of
policy as distinguished from the changes and
trends typically of interest to site managers
and researchers. Typically, researchers and
site managers think of changes and trends at
individual sites while policy makers think of
changes and trends in groups or populations
of systems. Detection of changes and trends
in characteristics affecting broad policy
issues requires repeated surveys over time
rather than intensive monitoring of individual
waterbodies. As planned, the National
Aquatic Resource Surveys are designed
to provide the data needed for detection
of changes and trends necessary for the
evaluation of policy. Repeated measurements
on at least a good portion of the same
individual lakes in the regional surveys will,
in time, provide the needed information for
detection of changes and trends necessary for
the evaluation of regional practices. This first
survey of lakes and reservoirs provides clear
information on current status but obviously
cannot, by itself, provide the necessary
information for changes and trends. The
National Lakes Assessment, however,
incorporated three features that begin to
provide decision makers with an initial
glimpse at what changes have occurred in
lakes. Over time, EPA intends to use further
analysis and future surveys to enhance the
trends analyses.
The first indication of change comes from
the analysis of a specific subset of lakes
that was the subject of a previous study.
While EPA does not have past probability
surveys of all lakes in the U.S., the Agency
and the states implemented the National
Eutrophication Survey (NES) in the 1970s
- a survey that included more than 800
lakes. The second example of changes uses
data external to the NLA. This information
is based on data in a regional study of
acidic lakes in a specific subpopulation of
interest, the northeastern U.S. Finally, a third
examination of change involves the use of
cores from the lake sediments. By examining
different cross sections within the core and
the microscopic algae present, analysts can
infer past conditions in each lake. Each of
these approaches is presented below.
-------
Chapter 7 Changes and Trends
Subpopulation Analysis of Change
- National Eutrophication Survey
Monitoring and surveillance programs
have in the past often dealt with site-
specific questions of ecosystem condition,
thus concentrating on single lakes or small
groups of lakes. For example, specific sites
of interest are often regularly monitored for
nutrient levels, frequency of algal blooms,
fisheries, bacterial counts at swimming
beaches, etc. However, pressures on aquatic
systems across large geographic areas has
provided the impetus to assess lakes over
far wider regions. In response, the NES was
conducted in 1972-1976. While national in
scope, it was unlike the NLA in that it was
not a probability selection of lakes. Rather it
was a targeted selection of over 800 lakes,
designed to assess the trophic condition
(defined as the nutrient enrichment) of lakes
influenced by domestic wastewater treatment
plants (WWTP). The specific purpose of the
survey was to measure nutrient inputs from
all sources in the watershed relative to those
of the WWTP source to determine if WWTP
upgrades might be successful in modifying
the lake or reservoir trophic state.
For the NLA, a subset of 200 lakes from
the 1972-1976 NES survey was randomly
selected using the same probability design
principles from the broader survey. This
allows the condition of all 800 lakes from
the original NES survey to be inferred
from the subsample of 200 lakes from
2007. The phosphorus levels, chlorophyll-a
concentrations, and trophic condition of
the NES population in 2007 can then be
compared to what was observed in the 1970s
to determine how these metrics have changed
over the last thirty-plus years.
When making comparisons between then
and now, some design differences between
the two studies must be considered. The NLA
sampling consisted of a single, mid-summer
integrated water sample at the deepest spot
in the lake and from just below the surface to
a depth of up to 2m (a sampling tube). The
NES sampling consisted of sampling several
sites on the lake as well as the inlets and
outlets. NES sampling also included a site
at the perceived deepest spot in the lake.
Sampling was done with a depth-specific
sampler (bottle) at just below the surface and
at 1-2 m depth intervals. Analysts compared
the integrated sample NLA chlorophyll
concentrations and NES samples taken at the
site nearest the NLA site and from depth(s)
that most nearly mimicked the depth of the
NLA integrated depth sample. The accuracy
and precision of chemical analytical results
are considered comparable to each other
based on the methods and the quality
assurance of both surveys.
The NLA analysts looked at changes
in the NES lakes over the past thirty-plus
years using two approaches: by comparing
concentration levels of key indicators and
by examining trophic status. In both cases,
researchers are able to estimate the number
and percentage of NES lakes that showed
a change since the original sampling in the
1970s. It is worth noting that this type of
analysis provides an estimate of net change
but little information on change in individual
-------
Chapter 7 Changes and Trends
Change in Phosphorus
NES Lakes 1972 -2007
Figure 34. Proportion of NES lakes that exhibited
improvement, degradation, or no change in
phosphorus concentration based on the comparison
of the 1972 National Eutrophication Survey and the
2007 National Lakes Assessment
Change in Trophic State
(Chlorophyll)
Degraded
Unchanged.
Improved
Figure 35. Proportion of NES lakes that exhibited improvement,
degradation, or no change in trophic state based on the
comparison of the 1972 National Eutrophication Survey and the
2007 National Lakes Assessment.
lakes.
Phosphorus levels have decreased in
more than 50% of the NES lakes (403); for
almost 24% (189) no change was detected.
An increase in phosphorus levels was seen in
26% of the lakes (207) (Figure 34).
Trophic status based on chlorophyll-a also
changed. Trophic status improved in 26%
(184) of the lakes, and over half (51% or 408
lakes) of the NES lakes remained unchanged
with respect to their tropic state. Trophic
state degraded in 23% (208) of the NES lakes
(Figure 35). Specifically, using chlorophyll-a
as the indicator of trophic state, 49% of
the lakes (394 lakes) in NES were classified
as hypereutrophic in 1972. In 2007, that
number had fallen to 35% (279) of the lakes.
In 1972, just over 5% of the lakes were
classified as oligotrophic and by 2007, over
14% of the lakes (117) were classified as
oligotrophic (Figure 36).
Subpopulation Analysis - Trends
in Acidic Lakes in the Northeast
A similar approach was taken for
lakes that are either acidic or sensitive
to acidification, as assessed under the
EMAP Temporally Integrated Monitoring of
Ecosystems/Long Term Monitoring (TIME/
LTM) program. During the 1980s, the
National Surface Water Survey was conducted
nationally of lakes in acid sensitive regions.
The NLA results show that acidification of
lakes affects a very small number of lakes
nationally. However, in certain regions of
the country, the problem is of concern,
particularly when lakes smaller than 10 acres
(4 hectares) are included. The results below
are another example of the use of surveys
through time to track changes and trends
in population of lakes. These results have
been previously reported in the EPA's Report
on the Environment and the peer-reviewed
literature.
-------
Chapter 7 Changes and Trends
National Eutrophication Survey Lakes
19728. 2007
5.4%
Oligotrophic
146%
Mesotrophic
Eutrophic
Hypereutrophic
49%
34.9%
43
117
233
189
130
215
394
279
Figure 36. Percentage and
number of NES lakes estimated
in each of four trophic classes
in 1972 and in 2007 based on
chlorophyll-a concentrations.
40 60
Percentage of Lakes
80
100
^m 1972-NES
Between the early 1990s and 2005, the
acid neutralizing capacity (ANC - a measure
of a lakes ability to withstand acidification) in
lakes in the Adirondack Mountains increased
to a degree where many water bodies that
were considered "chronically acidic" in
the early 1990s were no longer classified
as such in 2005 (Figure 37). Specifically,
between 1991-1994 and 2005, the percent
of chronically acidic waterbodies decreased
in the Adirondack Mountains (from 13.0%
to 6.2%). Additionally, acid-sensitive lakes
in New England were beginning to show a
decrease in acidity. The percent of chronically
acidic lakes in this region decreased from
5.6% in 1991-1994 to 4.3% in 2005. This
trend suggests that lakes in these two regions
are beginning to recover from acidification,
though acidic surface waters are still found in
these regions.
I 1 2007 NES in NLA
The trend of increasing ANC in the
Adirondack Mountains and New England
between the early 1990s and 2005
corresponds with a decrease in acid
deposition in each of these regions and
reduced air emissions of the main precursors
to acid deposition, which are sulfur dioxide
and nitrogen oxides.
-------
Chapter 7 Changes and Trends
Percentage of Acidic Lakes
Adirondacks
New England
Figure 37. Change in
percentage of lakes that
are chronically acidic in
the Adirondack Mountains
and New England.
10 15
Percentage of Lakes
25
Sediment Core Analysis of Change
A different approach was used in the third
examination of change. The NLA incorporated
paleolimnological analyses, a technique that
uses lake sediment cores to obtain insights
about past conditions. NLA analysts looked at
thin slices of cores and identified the diatom
silica casings. The community of diatoms
present in each slice gives clues to the
chemical and physical conditions in the lake
when that layer was deposited. Researchers
developed models relating the diatom
community to lake chemistry characteristics
such as total phosphorus and to lake physical
characteristics such as clarity. Using these
relationships, the diatoms in deeper layers
of the sediment can be identified and the
chemical conditions present at that point in
time can be inferred from the model. This
technique was used very effectively during
studies of acidification in lakes during
the 1980s. Individual states and other
organizations have also used sediment cores
in this manner on more localized/regional
scales to improve our understanding of what
lakes were like in the past.
EPA piloted this technique for application
at a national scale which provides a means
of examining temporal change in a subset
of all lakes included in the NLA across the
lower 48 states. In the field, the top layer of
the sediment core was collected along with
a layer deep in the core. Because of the
expense, the deep section of the core was
not dated to confirm its age. Instead, NLA
researchers used independent techniques,
their own expertise, and that of regional
experts to determine whether the cores were
sufficiently deep for NLA purposes. This
approach is a less reliable, but less costly
means of estimating the age of the cores.
National Lakes Assessment: A Collaborative Survey of the Notion's Lakes
-------
Chapter 7 Changes and Trends
The bottom layer of the sediment
cores was not collected for man-made
lakes because it was presumed sediment
cores in these more recent lakes would not
represent a pre-industrial condition. Three
hundred ninety-two lakes, representing
34% of the target population are in this
category and therefore were not evaluated.
Of the remaining natural lakes, 334 lakes,
representing about 22% of the target
population, were not evaluated because
the core length was insufficient. That left
426 lakes, representing 55% of the target
population, where estimates of change were
possible. While results from this approach
are presented below, further analyses will
be necessary to determine if sediment core
dating should be included in future lake
surveys. Issues for consideration include
evaluating:
Whether the approach used is sufficiently
robust to identify cores reaching pre-
industrial times across the country;
Whether the assessment of change
in a relatively small subset of lakes merits
the effort expended in the context of a
national survey; and
Whether alternative coring and/or dating
approaches should be considered for
future iterations of the NLA.
Even though the percentage of target
population is less than optimum, some
information can be gleaned from the data.
Results from the cores selected based on the
approach described above showed that an
estimated 17% of lakes in the lower 48 states
showed no significant change in inferred total
phosphorus between the bottom of the core
and the top of the core. A decrease in total
phosphorus was estimated to have occurred
in 12% of the lakes while almost 7% of lakes
were estimated to have experienced an
increase in total phosphorus. The pattern in
changes for total nitrogen differs somewhat.
Nationally, the percentage of lakes showing
no change between the top and bottom of the
core is less than 5%. Sixteen percent of the
lakes showed an increase in total nitrogen
while 18% showed a decrease in total
nitrogen.
These results from the NLA comparison
between the top and bottom of the sediment
cores suggests that many lakes may have
lower total phosphorus and total nitrogen
levels now than they once did. This is
unexpected for many (but not all) of the
lower 48 states. Without dating the cores,
more information and analysis are needed in
explaining these results.
National Lakes Assessment A Collaborative Survey of the Notion's Lakes
-------
HIGHLIGHT
Climate Impacts on Lakes
Warmer Temperatures and Lake Condition
The preponderance of information indicates that the planet is warming and significant changes in
climate are expected around the globe. The International Panel on Climate Change (IPCC) unequivocally
attributes the climate change to human activities that have increased greenhouse gases in the
atmosphere. The United States alone saw an increase
of 1° (F) over the last century. Most of the warming
has occurred in the last three decades and the largest
observed warming across the country has taken place
in the winter months. In southern areas, surface water
temperatures are surpassing those of air temperatures,
while in the north, there is ample evidence of earlier
ice-out dates. For lakes, these changes will impact
reservoirs and drinking water sources, hydroelectric
power facilities, irrigation regimes, shipping and
navigation, and recreational opportunities. From
an ecosystem standpoint, warmer lakes will result
in changes in water depth, thermal regime, nutrient
loading, retention time, mixing and oxygen availability,
and suspended sediments - all of which will alter
habitat suitability and lake productivity.
Changes in the Upper Midwest The Great Lakes
While scientists generally agree that the nation will get slightly wetter over the next century,
precipitation trends at a regional level are uncertain. In many areas, however increased rainfall could
be offset by increased evaporation, both in terms of soil moisture and surface water. The Great Lakes,
which hold 18% of the world's fresh surface water, are being watched carefully. Many agree that warming
trends throughout the region will lead to a climate more comparable to the Deep South thus making the
lakes themselves smaller and muddier. Since 1988, temperature in Lake Erie has risen 1° (F) and while
predictions vary, some researchers forecast that by 2070, lake level will fall about 34 inches and surface
area will shrink 15%. This scenario would leave 2,200 square miles of new land exposed. Lower water
levels and less ice cover will lead to more sediment delivery, and therefore more algae and potentially
more waterborne diseases. Excessive algal blooms can affect aquatic life and harm animals and humans.
Climate changes will also affect fish populations and zooplankton communities due to the disruptions in
lake dynamics such as the timing and severity of ice-cover, winter-kill and spring/fall turn-over.
Changes in the Southwest - Lake Tahoe and Lake Mead
Persistent drought conditions; increased extreme rainfall events; more wildfires; and heightened
flooding, runoff and soil erosion are all expected to afflict the already arid southwest. Since 1988, the
average surface water temperature of Lake Tahoe has increased by 1° (F). Other signs of persistent
warming are decreased snowfall, later snowfall, and earlier snowmelt. In Tahoe City, Calif, the percentage
of precipitation falling as snow has dropped from 52% in 1910 to 35% in 2007 and since 1961, peak
78
National Lakes Assessment A Collaborative Survey of the Nation's Lakes
-------
snowmelt throughout the lake region has shifted earlier by two and a half weeks. In Tahoe: State of
the Lake Report 2008, researchers reported that algal growth, considered an indicator of warming's
acceleration, has increased rapidly with concentrations now five time what they were in 1959. Levels of
nitrogen and phosphorus deposited from the Angora forest fire (also considered a climate indicator) also
were 2-7 times greater than normal.
Fluctuations in precipitation and snowpack have critical impacts on
life in the desert. In Nevada, the water level in Lake Mead is steadily
dropping and with it the hydroelectric production capacity by Hoover
Dam. Studies cited by the National Conference of State Legislatures
and Center for Integrative Environmental Research (2008) indicate
that there is a 10% chance that Lake Mead could dry up by 2021 and
a 50% chance it will be gone by 2050. Lake Mead provides drinking
water for over 2 million people and generates electricity for over 1.3
million. Water-based recreation brings in more than $1 billion to the
area's economy. Major changes in annual precipitation and snowpack
are proving difficult for reservoir managers who must balance winter
flooding with maximum capture and storage for summer water needs all within the context of overall
declining water levels.
What the Experts Say
How a changing climate will impact the country's lakes is far from understood and not easy to grasp.
The Climate Change Science Program, in its 2008 report, underscores that most observed changes in
water quality across the continental U.S. are likely attributable to causes other than climate change and
are instead primarily due to changes in pollutant loadings. Notwithstanding, there is general agreement
with the IPCC (2007) conclusion that higher water temperatures, increased precipitation intensity and
longer periods of low levels are likely to exacerbate many forms of water pollution, with impacts on
ecosystem integrity, and water system reliability and operating costs. Both groups agree that a mix of
mitigation and adaptation will be necessary to address the impacts.
79
Notional Lakes Assessment A Collaborative Survey of the Nation's Lakes
-------
CHAPTER 8.
CONCLUSIONS AND IMPLICATIONS
FOR LAKE MANAGERS
IN THIS CHAPTER
Overall Findings and Conclusions
Implications for Lake Managers
-------
Chapter 8 Conclusions and Implications for Resource Managers
Chapter 8
Conclusions and
Implications for
Resource Managers
Overall Findings and Conclusions
The NLA offers a unique opportunity to
frame discussions and planning strategies
based on environmental outcomes and across
jurisdictional lines. It serves as a first step
in the evaluation of the collective successes
of management efforts to protect, preserve,
or restore water quality. Attributable risk
analyses can serve as a useful tool to help
prioritize individual stressors. As EPA and
its partners repeat the survey, the NLA will
be able to track changes in water quality
over time for lakes as a whole rather than
just for a few individuals, thus advance our
understanding of important regional and
national patterns in water quality, and speak
to the cumulative effectiveness of our national
water program.
Taken together, the results of the NLA provide
a broad range of information necessary to
understand the condition of our nation's lakes
and some of the key stressors likely to be
affecting them. The results are especially
important because they establish a national
baseline for future monitoring efforts which
can be used to track statistically-valid
trends in lake condition. These stressors to
lake systems are now placed in context of
their relative importance for restoring and
maintaining lake integrity.
Condition of the Nation's Lakes
The results of the survey provide
information relating to the fundamental
question of "what is the condition of the
nation's lakes?" The NLA reports on condition
in three important ways. Biological indicators
are especially useful in evaluating national
condition because they integrate stress of
combined problems over time. The NLA shows
that 56% of the nation's lakes are in good
condition, 21% are in fair condition, and 24%
are in poor condition based on a measure
of planktonic O/E taxa loss. Recreational
suitability based on cyanobacteria (blue-
green algae that can produce toxins that
pose threats to human health) levels are
National Lakes Assessm(
Nation s Lakes
-------
Chapter 8
Conclusions and Implications for Resource Managers
in the low risk category in 72% of lakes.
Finally, trophic status results based on
chlorophyll-a concentrations find that 20%
of lakes are hypereutrophic while 80% are in
categories that exhibit lower levels of nutrient
enrichment.
Ecoregional assessments reveal broad-
scale patterns in lake condition across
state lines and across the country. Again
using biological integrity as the primary
characteristic of lake health, the Northern
Appalachian Plateau, the Upper Midwest and
the Western Mountains ecoregions have the
highest proportion of lakes in good condition
- over half of the lakes in these regions are
classified as good.
While it is too early in the survey program
to determine if lake condition is improving,
NLA analysts were able to examine changes
in one set of lakes. When comparing these
results to a subset of lakes sampled of more
than thirty years ago, it is encouraging to see
that phosphorus concentrations decreased
in 50% of the NES lakes and remained
unchanged in 24% of the lakes. In essence
this mean that phosphorus level in nearly
two-thirds of these lakes remained the same
or even improved despite growth of the U.S.
population.
Major Physical and Chemical
Stressors to Biological Quality
The NLA results show that of the
indicators measured in the study, degraded
lakeshore habitat around the lake is the most
significant stressor to poor biological integrity
across the country. Using this as the primary
habitat indicator, just under half of the
country's lakes (45%) are in good condition.
The NLA results also show that lakes in poor
condition for habitat are 3 times more likely
to be in poor biological condition. Another
indicator of habitat examined was evidence
of human activities. From the standpoint of
human disturbances along lakeshores, just
one-third (35%) of the country's lakes are in
good condition. NLA results also show that the
proportion of lakes with shoreline disturbance
and associated habitat alterations does not
show any significant ecoregion variability.
In addition to exhibiting good biological
conditions, about half of the lakes in the
Northern Appalachians, the Upper Midwest
and the Western Mountains ecoregions, plus
the Temperate Plains ecoregion are in good
habitat condition relative to other ecoregions
across the country.
Nutrients in the form of phosphorus and
nitrogen are the second most important
stressor to lake biological health. Fifty-
eight percent of lakes are in good condition
relative to total phosphorus levels and
54% are in good condition relative to total
nitrogen. Lakes in poor condition for either
of these stressors are twice as likely to be in
poor biological condition. Yet, unlike habitat
condition, nutrient levels vary widely across
the country. The Northern Appalachians
ecoregion has the highest percentage of lakes
in good condition relative to total phosphorus
(TP) and total nitrogen (TN) (79% forTP and
88% for TN) while the Temperate Plains (38%
for TP and 27% for TN) and the Northern
Plains (22% for TP and 9% for TN) ecoregions
have the lowest.
-------
Chapter 8 \ Conclusions and Implications for Resource Managers
Implications for Lake Managers
While survey results fill key informational
gaps in regional and national monitoring
programs by generating estimates of the
condition of water resources, evaluating the
prevalence of key stressors, and documenting
trends in the population waters over time,
they do not address all management concerns
at all scales. For example, the surveys do
not address causal factors or sources of
stress. For water resource managers and
city planners, any effort to reduce stresses
and improve water quality entails confronting
the source(s) of the stress (such as energy
generation, agricultural production, or
suburban development) and working together
toward implementing viable but often difficult
solutions.
Address Major Lake Stressors
State lake management programs
increasingly report that development
pressures on lakes are steadily growing. The
NLA findings show that, local, state, and
national initiatives should center on shoreline
habitats, particularly vegetative cover, and
nutrient loads to protect the integrity of lakes.
The findings of the four physical habitat
indicators show that poor habitat condition
imparts a significant stress on lakes and could
suggest the need for stronger management of
lakeshore development at the all jurisdictional
levels. Of the four, degradation of lakeshore
habitat cover is the most important stressor
of lakes and the attributable risk analysis
suggests that eliminating the effects
of poor lakeshore habitat cover could
improve the biological condition in 40%
of lakes. Development and disturbance
along lakeshores (such as tree removal and
residential construction) impacts the integrity
of lakeshore and shallow water habitats,
affecting terrestrial and aquatic biota alike.
These NLA results support the continuing
need for national, state, and local efforts to
ameliorate the impacts of human activities
in and around lakes to protect the lake
ecosystem. EPA's Low Impact Development
(LID) program is one national-scale initiative
to address lakeshore development pressures.
Nutrients have been a longstanding
stressor of waterbodies in this country.
Nationally, over 40% of the lakes exhibit
moderate or high levels of nitrogen or
phosphorus concentrations. In addition,
regional hotspots are evident - in the
Temperate and Northern Plains nearly all
lakes have high levels of nutrients. The NLA
findings emphasize the need for continuing
implementation of Federal-State partnership
programs to control point and non-point
sources of nutrient pollution. This type of
information can be used to support and
enhance collaboration between jurisdictional
authorities and the use of programs such
as the Environmental Quality Incentives
Program and Conservation Reserve and
Enhancement Programs managed by USDA's
Natural Resources Conservation Service, and
the Clean Water Act Section 319 Program and
National Point Sources Discharge Elimination
System under the Clean Water Act.
Track Status and Trends Information
Lake managers should consider the
national trend information as well as the
ecoregional data in evaluating site specific
information in a broader context. Conducted
on a five-year basis, subsequent lake survey
results will help water resource managers to
assess temporal differences in the data and
perform trends analyses. Future surveys will
also help EPA and its partners to evaluate
national and ecoregional stressors to these
ecosystems, track changes, and explore the
relative importance of each in restoring or
maintaining waterbody health. Wide-area or
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 8 Conclusions and Implications for Resource Managers
regional changes in stressors over time can
potentially be linked to human factors such
as land use changes (e.g., development) or
natural causes (e.g., increased storm surges).
Implement Statewide
Statistical Surveys
Statistical survey designs provide water
resource managers and the public with
consistent, statistically-valid assessments of
all waters in the area of interest (nationally,
state-wide, etc.). Information provided by
these surveys can help managers monitor
the effectiveness of their lake restoration and
pollution control activities as well as target
resources and additional monitoring where
they are most needed. To date, 40 states
are implementing statistical surveys (Figure
38). These states have been successful in
leveraging their limited monitoring resources
and have gained state-wide insights into their
water resource quality. EPA encourages all
states to implement state-wide statistical
surveys.
States with statistical survey programs
are already using the results to develop
watershed-scale or site-specific protection or
restoration projects. Virginia, for instance,
has established an intensive water quality
monitoring program incorporating statistical
w Impact Development Protects Lake Quality
Low impact development (LID) is a set of approaches and practices that are designed to reduce
runoff of water and pollutants from the site at which they are generated. LID techniques manage water
and water pollutants at the source through infiltration, evapotranspiration, and reuse of rainwater,
preventing many pollutants from ever reaching nearby surface waters. LID practices include rain
gardens, porous pavements, green roofs, infiltration planters, trees and tree boxes, and rainwater
harvesting for non-potable uses such as toilet flushing and landscape irrigation. The primary goal of LID
is to design each development site to protect, or restore, the natural hydrology of the site so that the
overall integrity of the watershed is protected.
Development typically causes an imbalance in the natural hydrology of a watershed by replacing
pervious surfaces (e.g., fields, forests, wetlands etc.) with impervious surfaces (e.g.) rooftops, parking
lots, roads, etc.). This change in ground cover not only increases runoff because decreased infiltration,
but reduces the potential for the removal of nonpoint source pollutants.
By engineering terrain, vegetation, and soil features, LID practices promote infiltration of runoff
close to its source and help prevent sediment, nutrients, and toxic loads from being transported to
nearby surface waters. Once runoff is infiltrated into soils, plants and microbes can naturally filter and
break down many pollutants and restrict movement of others.
Implementing LID practices in watersheds will contribute to groundwater recharge, improve water
quality, reduce flooding, preserve habitat, and protect lake quality. In addition, LID practices increase
land value, the aesthetics and recreational opportunities, and public/private collaborative partnerships
while reducing stormwater management costs. For more information visit: http://www.epa.gov/owow/
nps/lid.
National Lakes Assessment; A Collaborative Survey of the Nation's Lakes
-------
Chapter 8 Conclusions and Implications for Resource Monogers
Use of Probability Surveys as a Component
of State Monitoring Program
HI
Status of State Use of Probability Surveys
^H Adopted state scale survey (40)
1550 Piloting/Investigating use of state scale survey (7)
j Not currently pursuing state scale survey (3)
August 25 2009
Figure 38. States with state-scale statistical surveys
sampling methods. South Carolina's
monitoring program includes a statistically-
based component to complement its targeted
monitoring activities. Each year a new
statewide set of statistical random sites
is selected for each waterbody type, i.e.,
streams, lakes/reservoirs, and estuaries.
The State of Florida also implements an
annual probabilistic monitoring program.
Their program will be an enhancement of its
2000 Status Monitoring Network a five-year
rotating-basin, statistical design sampling of
six water resources, including small lakes
(1-10 hectares) and large lakes (>10
hectares). Florida is currently in the fifth
year of the Network and will report its
findings in 2010. States with probabilistic
survey programs have found that state-wide
survey data provide more information and
more useful information than other types of
monitoring programs.
State-wide surveys can be leveraged with
the national survey and the information can
be used in conjunction with other existing
state monitoring programs to get a better
understanding of the state's waters. In the
same way that a lake association might relate
the conditions it measures in a particular
lake to other lakes, state/tribal managers can
relate the conditions of lakes statewide to
relevant ecoregional or national conditions.
For example, the State of Vermont compared
its lake's trophic status to the lakes in
the Northern Appalachian ecoregion and
nationwide (Figure 39). This assessment
shows that lakes in Vermont are more
oligotrophic than lakes at the NLA ecoregional
or national scale. Lake managers in states
with a statistical survey network can use
information such as this to target conditions
to which lakes should be managed.
National Lakes Assessment: A Collaborative Survey of th.
-------
Chapter 8 Conclusions and Implications for Resource Managers
Perspective From Different Spatial Scales
Trophic State
Vermont
Northern Appalachian
US (lower 48)
Figure 39. Comparison of lakes
by trophic state for Vermont
(VT), the Northern Appalachian
Ecoregion (NAP), and the Nation
(U.S. 48), based on chlorophyll-a.
40 60 80
Proportion of Lakes
Oligotrophic (< 2 ug/L) Mesotrophic (>2-7 ug/L)
Ei/trophic (>7 - 30 ug/L Hypereulrophic (> 30 ug/L)
100
Incorporate New and
Innovative Approaches
EPA is encouraging states, tribes, and
others to utilize NLA data and methods for
their own customized purposes. The NLA
provides lake managers with new tools and
techniques to adopt into existing programs.
Mangers are encouraged to consider the host
of new assessment indicators and methods
that are applicable within assessment
programs of any scale. For example, the
quantitative assessment of physical habitat
at the land-water interface is an area of
intensifying focus within the lakes community.
The NLA physical habitat assessment method
provides a ready approach that has already
been implemented by field crews across the
lower 48 states and Alaska. The resulting
data is readily reduced to four components
of habitat integrity that relate directly
to ecological integrity in lakes. For lake
assessment programs lacking a physical
habitat assessment component, the NLA
method provides a low-cost and information-
rich enhancement.
The incorporation of recreational
indicators within lake assessment programs
can also yield useful information to lake
managers. Public awareness of cyanobacteria
and related toxins is increasing, fueled in
part by an increasing number of beach
closures and related media reports. In
the NLA, while only a small proportion
of lakes exhibited moderate or high-risk
concentrations of microcystin, the proportions
of lakes with concentrations of chlorophyll-a
or cyanobacteria cells associated with the
development of elevated microcystin was
considerably greater. Routine monitoring of
chlorophyll-a, cyanobacterial cell counts, and/
-------
Chapter 8 Conclusions and /mp/icot/ons for Resource Monogers
or microcystin can be implemented using
a tiered approach tailored to the likelihood
of microcystin occurrence. Many states
are now adopting such programs, resulting
in greater protection of human health in
instances where cyanobacteria blooms may
limit swimming use.
Work Beyond
Jurisdictional Boundaries
Survey data on a national scale allows
for aggregation of data and comparability of
the results across several ecoregional levels.
Within each of these ecoregions, states often
share common problems and stressors to
shared watersheds. The NLA offers a unique
opportunity for adjacent states to work
together, establish coalitions, and put into
place collaborative actions that cross state
boundaries. As a starting point, EPA and
its state partners are working together to
develop approaches to monitoring that will
allow comparisons on a state-wide basis and
across state boundaries as well. EPA and the
states are committed to finding mutually-
beneficial and scientifically-sound ways to
integrate and exchange data from multiple
sources, as well as options to improve both
sample collection and analytical methods.
-------
HIGHLIGHT
State, Tribal, and Regional Lake Surveys:
Examples From Across the Country
State-wide Lake Assessments
Oklahoma: Oklahoma was one of several states that chose to add to the number of nationally selected
lake sites within its boundaries to achieve a state-wide assessment. Oklahoma is looking into using
National Lakes Assessment (NLA) survey data for further development of nutrient and biological criteria,
incorporating new parameters into its established monitoring program, and nesting a probability based
survey into its fixed station rotation.
Michigan: Twenty-nine Michigan lakes were randomly selected as part of the NLA. To allow for a state-
scale assessment, the state added 21 additional randomly-chosen lakes. Michigan's surveyed lakes
ranged from an unnamed 10-acre lake in Clare County to 13,000-acre Gogebic Lake, in Gogebic County.
The state will analyze its lake data set for an evaluation of
the condition of Michigan's inland lakes based on the national
survey assessment tools.
Oregon: Oregon sampled 32 lakes across the state as part
of the NLA. In Oregon, the results from the 2007 NLA will
help answer two key questions about the quality of lakes,
ponds and reservoirs: What percent of Oregon's lakes are
in good, fair or poor condition for key indicators of nutrient
status, ecological health and recreation? What is the relative
importance of key lake "stress factors" such as nutrients and
pathogens? The random design took field crews to a wide
variety of sites. Elevation at the target lakes ranged from 30
feet to 7,850 feet. Lake depths ranged from 1 meter to 128
meters (Waldo Lake); maximum sampling depth, however,
was 50 meters. The most difficult lake to reach was Ice
Lake in the Eagle Cap Wilderness, which required the use
of an outfitter and horses for the eight-mile and 3,300-foot
elevation gain journey.
Enhancing Lake Monitoring for the
Lac du Flambeau Tribe, Wisconsin
Ice Lake in the Eagle Cap Wilderness
(taken from http://www.deq.state.or.us/lab/wqm/docs/08-LAB-009.pdf)
The Lac du Flambeau Tribe is using the NLA study to enhance its own water program. The ability to
develop protective site-specific water quality criteria and assess lake health is limited when available data
covers only a small geographic area such as the Lac du Flambeau Reservation. Tribal participation in the
NLA enabled the Tribe to compare reservation lake data to national and regional lake health. The Tribe
used the NLA protocols for physical habitat, water chemistry, and vertical water profiles on an additional
11 lakes within the reservation. These data are being entered into EPA's Water Quality Exchange (WQX)
using an excel template to ensure data uniformity for comparison. The Tribe will develop lake report
Notional Lakes Assessment A Collaborative Survey of the Nation's Lakes
88
-------
cards for the general public, managers, and decision makers assessing the health of reservation lakes
as compared to national and regional lake health. The Tribe will also be able to evaluate development of
criteria using these data.
Assessing Prairie Potholes: A Collaborative Effort.
The Prairie Pothole Region (PPR) crosses the north central U.S. and Canada and includes nearly 8,000
prairie pothole lakes. Prairie pothole lakes are intrinsically shallow and defined as natural lakes with
where 80% or more of the lake is less than 15 feet deep. PPR lakes are part of a major waterfowl fly-
way and are a valuable regional and national resource. In
order to more fully understand this unique ecosystem, North
Dakota, Iowa, Minnesota, South Dakota, Montana, USGS,
and EPA undertook an assessment of these lakes. Analysts
have found that nutrient and chlorophyll-a levels in PPR
lakes are quite high as compared to the nation's lakes. A
combination of high nutrient levels, elevated algae growth,
low transparency, presence of roughfish, and broad, wind-
swept basins serve to limit rooted plant growth. Maintaining
rooted plant growth is important for prairie pothole health.
More detailed information on the results of the Prairie Pothole ^'
survey will be provided in the NLA supplemental report. :.+~-~*-.,i,..
1
Photo courtesy of Wes Weissenburger
89
National takes Assessment A Collaborative Survey of the Nation's Lakes
-------
CHAPTER 9.
NEXT STEPS FOR
THE NATIONAL SURVEYS
IN THIS CHAPTER
Supplemental Reports
Tools and Other Analytical Support
Future National Assessments
-------
Chapter 9
Next Steps for the National Surveys
Chapter 9
Next Steps for the
National Surveys
EPA is committed to continually enhancing
the National Aquatic Resource surveys in
order to improve the quality and quantity
of information we need to understand the
condition of the aquatic environment and
how it is changing over time. As technologies
advance, future surveys and collaborations
can also lead to new indicators, new
monitoring approaches, and new water
resource management programs and policies.
With the publication of this report, the
lakes survey moves into a design/planning
phase in preparation for the next survey in
2012. This phase will incorporate lessons
learned from the first lakes survey, other
national surveys, and state, tribal and local
experiences. Additionally, EPA anticipates
that states and other partners will continue
to utilize data from the first lakes survey
and issue supplemental reports based on
their findings.
During 2010, EPA and its state and tribal
partners will take stock of the survey
and begin planning for 2012. Issues for
discussion may include changes to the
design, field methods, equipment, laboratory
methods, and/or analyses procedures.
Other items include improving reference site
selection, refining regionally representative
reference sites, and adding more reference
sites to the survey. Consideration will be
given not only to how alternate approaches
will improve future data, but how we can
ensure comparability to the initial baseline.
Lakes
2006
Design
2007
Field
2008
Lab and
Data
Analysis
National Lakes Assessment: A Collaborative Survey of t/ie Nation's Lakes
-------
Chapter 9 Next Steps for the National Surveys
Supplemental Reports
The NLA included data collection for
several indicators for which analysis could not
be completed in time for this report. These
included benthic macrinvertebrates, sediment
mercury, and enterococcus. Analysts are
currently developing macroinvertebrate IBIs
and O/E models to add to our understanding
of biological integrity of lakes. Sediment
mercury samples are still in the data analysis
phase, as is the enterococcus dataset. EPA
plans to produce an addendum to this
report with the macroinvertebrate, sediment
mercury, and enterococcus findings.
In the next few years, EPA plans to
continue additional analyses of the survey
data to develop tools and strategies that will
provide a better understanding of lakes and
water resources in general. One important
undertaking will be to conduct an in-depth
analysis of the relationship between lake
condition, stressors, and management actions
such as point and nonpoint controls and other
restoration activities. EPA plans to publish its
progress and findings in interim lake survey
reports.
Tools and Other
Analytical Support
The next two years will also provide a
unique opportunity for states to tailor their
own statewide program to complement the
national program. Extensive discussion
during the research and design phase will
focus on ways to leverage and integrate
national and state-scale surveys. This
approach will improve the efficiency and
value investment in monitoring aimed at
understanding the condition of the nation's
water resources. One EPA near-term project
will be to work with the states to develop
tools that can be used to re-create the
survey for state-wide assessments and for
customized purposes. EPA is committed to
providing technical support to assist states,
tribes and other partners in using these tools.
Such an "assessment tool kit" might include
IBI or O/E model development, habitat data
analysis techniques, decision-support tools,
and web-based trainings session.
Future National Assessments
EPA and its state, tribal and federal
partners expect to continue to produce
national assessments on a yearly cycle.
Rivers and streams sampling was completed
in 2008 and 2009, with a report due out in
2011. A national coastal assessment report
will be published in 2012 based on field
sampling 2010. Wetlands will be surveyed in
2011, followed by national reporting in 2013.
In 2012, field sampling for lakes will occur
again and the assessment report that
follows in 2014 will evaluate changes in
biological condition and key stressors.
The surveys will then continue with changes
and trends becoming a greater focus for
each resource type.
The continued utility of these national
surveys and their assessment reports
depends on continued consistency in design,
as well as field, lab and assessment methods
from assessment to assessment. However,
the surveys should also provide flexibility that
allows the science of monitoring to improve
over time. Maintaining consistency while
allowing flexibility and growth will continue to
be one of the challenges that will be faced in
the coming years.
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 9
Next Steps for the National Surveys
This national lakes survey would not
have been possible without the involvement
of hundreds of scientists working for state,
tribal, and federal agencies and universities
across the nation. Future National Aquatic
Resource Surveys will continue to rely on
this close collaboration, open exchange of
information, and the dedication, energy,
and hard work of its participants. EPA
will continue to work to help its partners
translate the expertise they gained through
these national surveys to studies of their
own waters. It also will work to ensure that
this valuable and substantial baseline of
information be widely used to evaluate the
success of its efforts to protect and restore
the quality of the Nation's waters.
National Lakes Assessment: A Co/laborative Survey of the Nation's Lakes
-------
Acronyms
Acronyms
ANC Acid Neutralizing Capacity
CPL Coastal Plains
CWA Clean Water Act
DO Dissolved Oxygen
DOC Dissolved Organic Carbon
EMAP Environmental Monitoring and Assessment Program
EPA Environmental Protection Agency
CIS Geographic Information System
IBI Index of Biological Integrity
ITIS Integrated Taxonomic Information System
LDCI Lake Diatom Condition Index
NAP Northern Appalachians
NARS National Aquatic Resource Surveys
NES National Eutrophication Study
NHD National Hydrography Dataset
NLA National Lakes Assessment
NLCD National Land Cover Dataset
NPL Northern Plains
O/E Observed/Expected
ORD Office of Research and Development, EPA
OW Office of Water, EPA
PPR Prairie Pothole Region
QA/QC Quality Assurance/Quality Control
QAPP Quality Assurance Project Plan
qPCR Quantitative Polymerase Chain Reaction
REMAP Regional Environmental Monitoring and Assessment Program
SAP Southern- Appalachians
SPL Southern Plains
TIME/LTM Temporally Integrated Monitoring of Ecosystem/Long Term Monitoring
TMDL Total Maximum Daily Load
TPL Temperate Plains
TN Total Nitrogen
TP Total Phosphorus
UMW Upper Midwest
USDA U.S. Department of Agriculture
USGS U.S. Geological Survey
WMT Western Mountains
WQX EPA's Water Quality Exchange
WWTP Wastewater Treatment Plant
XER Xeric
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Glossary of Terms
Glossary of Terms
Acid Neutralizing Capacity (ANC): A lake's ability to adapt to, i.e. neutralize, increases in
acidity due to acidic deposition from anthropogenic sources (automobile exhausts, fossil fuels) and
natural geologic sources.
Attributable risk: Magnitude or significance of a stressor. Is determined by combining the
relative extent of a stressor (prevalence) and the relative risk of the stressor (severity).
Benthic macroinvertebrates: Benthic meaning "bottom-dwelling". Aquatic larval or adult
insects, crayfish, worms and mollusks. These small creatures live on the lake bottom attached to
rocks, vegetation, logs and sticks, or burrow into the sediment.
Biological assemblage: Key group or community of plant or animal being studied to learn
more about the biological condition of water resources.
Biological integrity: State of being capable of supporting and maintaining a balanced
community of organisms having a species composition, diversity, and functional organization.
Chlorophyll-a: A type of plant pigment present in all types of algae sometimes in direct
proportion to the biomass of algae. A chemical indicator used to assess trophic condition.
Complexity: Used to describe the diversity and intricacy of an ecosystem. A complex habitat is
one that has a wide range of different niches for optimum growth and reproduction for both plants
and animals.
Condition: State or status of a particular indicator. For example, the biological condition of a
lake is the status of a biological assemblage, such as diatoms. Often measured against a reference
value or threshold.
Ecoregions: Ecological regions that are similar in climate, vegetation, soil type, and geology;
water resources within a particular ecoregion have similar natural characteristics and similar
responses to stressors.
Epilimnion: The uppermost, warmest, well-mixed layer of a lake during summertime.
Euphotic zone: The uppermost layer of the lake defined as the depth at which light penetrates.
Eutrophic: See Trophic state.
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Glossary of Terms
Eutrophication: The process of increased productivity of a lake or reservoir as it ages. Often this
process is greatly accelerated by human influences and is termed cultural eutrophication.
Hypereutrophic: See Trophic state.
Hypolimnion: The lower, cooler layer of lake during the summer.
Lakes Diatom Condition Index (LDCI): The sum of individual measures of a diatom
assemblage, such as number and composition of taxa present, diversity, morphology, and other
characteristics of the organisms.
Limnological: Of or pertaining to the study of fresh waters.
Littoral zone: The water's edge. Shallow water extending from the shoreline lakeward to the
greatest depth occupied by rooted plants.
Macrophyte: Litterally meaning "large plant." An aquatic plant that can grow emergent,
submergent or floating.
Mesotrophic: See Trophic state.
National Hydrography Dataset: Comprehensive set of digital spatial data that contains
information on surface water features across the U.S.
Nutrients: In the context of the NLA, substances such as nitrogen and phosphorus that are
essential to life but in excess can overstimulate the growth of algae and other plants in aquatic
environments. Excess nutrient can come from agricultural and urban runoff, leaking septic
systems, sewage discharges and similar sources.
O/E (Observed/Expected) Ratio of Taxa Loss: A comparison of the number of taxa that
are observed (O) at a site relative to the number of taxa expected (E) to exist for a site of similar
nature. The taxa expected at individual sites are based on models developed from data collected
at reference sites.
Oligotrophic: See Trophic state.
Pelagic zone: The open area of a lake, from the edge of the littoral zone to the
center of the lake.
Primary productivity: The production of organic compounds from atmospheric or aquatic
carbon dioxide, principally through the process of photosynthesis. All life on earth is directly or
indirectly reliant on primary production. In aquatic ecosystems, the organisms responsible for
primary production are the phytoplankton, and form the base of the food chain.
Notional Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Gfosso/y of Terms
Probability-based design: A type of random sampling technique in which every site in the
population has a known probability of being selected for sampling. Results from the sampled sites
can be used to represent the population as a whole.
Profundal zone: The deepest part of the lake located below the range of effective light
penetration.
Reference condition: The least-disturbed condition available in an ecological region,
determined based on specific criteria, and used as the benchmark for comparison with the
surveyed sample sites in the region.
Regionally-specific reference: A subset of the reference condition based on reference lake
sites of similar type and geography. For ecoregional assessments, the lakes are only compared to
the particular reference lakes that are similar for that area.
Relative extent: The relative prevalence of a specified condition (such as poor) for a stressor
or biological indicator. A stressor with a high relative extent means that it is relatively widespread
when compared to other stressors.
Relative risk: The severity of the stressor. Like attributable risk and relative extent of the risk,
this term is used to characterize and quantify the relative importance of the stressor. Stressors
with low relative extent and high relative risk are called "hot spots".
Riparian zone: The banks or shoreline of a lake or waterbody.
Riparian or Shoreline disturbance: A measure of the evidence of human activities alongside
lakes, such as roadways, dams, docks, marinas, crops, etc.
Riparian vegetative cover: Vegetation alongside lakeshore. Intact riparian vegetative cover
reduces pollution runoff, prevents streambank erosion, and provide shade, food, and habitat for
fish and other aquatic organisms.
Secchi transparency: A measure of the clarity of water obtained by lowering a black and white,
or all white, disk (Secchi disk) into the water until it is no longer visible. Measured in
feet or meters.
Stressors: Factors that adversely affect, and therefore degrade, aquatic ecosystems. Stressors
may be chemical (e.g., excess nutrient, pesticides, metals), physical (e.g., pH, turbidity, habitat),
or biological (e.g., invasive species, algal bloom).
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Glossary of Terms
Stressor-response: Change in biological condition due to the presence of one or
more stressors.
Taxa: Taxonomic grouping of living organisms, such as family, genus or species, used for
identification and classification purposes. Biologists describe and organize organisms into taxa in
order to better identify and understand them.
Threshold: The quantitative limit or boundary. For example, an assessment threshold is the
particular percentage of the reference condition or cut-off point at which a condition is considered
good, fair or poor.
Trophic State: Meaning "nourishment." Used to describe the level of productivity of a lake.
Oligotrophic: A nutrient poor lake. Describes a lake of low biological productivity and high
transparency or clarity.
Mesotrophic: A lake that is moderately productive.
Eutrophic: A well-nourished lake, very productive and supports a balanced and diverse array
of organisms. Usually low transparency due to high algae and chlorophyll-a content.
Hypereutrophic: Characterized by an excess of nutrients. These lakes usually support algal
blooms, vegetative overgrowth, and low biodiversity.
Watershed: A drainage area or basin in which all land and water areas drain or flow toward a
central repository such as a lake, river or the ocean.
Notional Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Sources and References
Sources and References
Bergstrom, J., K. Boyle, C. Job, and M. Kealy. 1996. Assessing the Economic Benefits of Ground
Water for Environmental Policy Decisions. Water Resources Bulletin 32(2):279-291.
Carlson, R.E. 1977. A Trophic State Index for Lakes. Limnology and Oceanography. 22:361-369.
Driscoll, C. D. Evers, K.F. Lambert, N. Kamman, T. Holsen, Y-J. Han, C. Chen, W Goodale/T. Butler,
T. Clair and R. Munson, 2007. Mercury Matters: Linking Mercury Science with Public Policy in the
Northeastern United States. Hubbard Brook Research Foundation. 2007. Science Links Publication.
Vol. 1, No. 3.
Egan, K. J., J. Herriges, C.. Kling, and J. Downing. 2009. Valuing Water Quality as a Function of
Water Quality Measures. American Journal of Agricultural Economics 91(1): 106-123.
Engel, S. and J. Pederson. 1998. The Construction, Aesthetics, and Effects of Lakeshore
Development: a Literature Review. Wisconsin. Dept. of Natural Resources, Report 177. Madison,
Wisconsin http://digital.library.wisc.edu/1711.dl/EcoNatRes.DNRRepl77.
Executive Office of the President. 2005. National Acid Precipitation Assessment Program Report to
Congress: an Integrated Assessment. http://www.epa.gov/airmarkets/resource/docs/NAPAP.pdf .
Fisher, B., R. Kerry Turner, and Paul Morling. 2009. Defining and Classifying Ecosystem Services
for Decision Making. Ecological Economics 68(3): 643-653.
Graham, J., K. Loftin, and N. Kamman. 2009. Recreational Monitoring of Cyanobacterial Toxins in
the United States. Lakeline 28:2.
H. J. Heinz III Center for Science, Economics and the Environment. 2008. The State of the Nation's
Ecosystems, Measuring the Lands, Waters, and Living Resources of the United States. http://www.
heinzctr.org/ecosystems .
Lindon, M. and S. Heiskary. 2009. Minnesota National Lakes Assessment Project: Microcystin
Concentrations in Minnesota Lakes. MN Pollution Control Agency. S. Paul, MN. USA. http://www.
pea.state.mn.us/publications/wq-nlapl-OO.pdf.
Herlihy, A. S. Paulsen, J. Van Sickle, J. Stoddard, C. Hawkins, L. Yuan. 2008. Striving for
Consistency in a National Assessment: the Challenges of Applying a Reference-condition Approach
at a Continental Scale. J. N. Amer. Benthol. Soc. 27:4.
Karr, J.R. 1981. Assessment of Biotic Integrity Using Fish Communities. Fisheries (Bethesda)
6:21-27. http://www.epa.gov/bioiwebl/html/ibi-hist.html.
Mann, D.G. 1995. The Species Concept in Diatoms. Phycologia 38:437-495.
National Lakes Assessment A Collaborative Survey of the Nation's Lakes
-------
Sources and References
Merrell, K., E. Howe and S. Warren. 2009. Examining Shorelines, Littorally. Lakeline 29:1.
Millennium Ecosystem Assessment. 2003. Ecosystems and Human Well-being: A Framework
for Assessment. Island Press, Washington. D.C. http://www.millenniumassessment.org/en/
Framework.aspx.
National Academy of Public Administration. 2002. Understanding What States Need to Protect
Water Quality. Academy Project Number 2001-001. Prepared by the National Academy of Public
Administration for the U.S. EPA, Washington, D.C.
National Research Council. 2001. Assessing the TMDL Approach to Water Quality Management.
National Academy Press, Washington, D.C.
Olsen, AJ.., B.D. Snyder, L.L. Stahl, J.L. Pitt. 2009. Survey Design for Lakes and Reservoirs in the
United States to Assess Contaminants in Fish Tissue. Environ. Monitoring Assess. 150:91-100.
Omernik, J.M. 1987. Ecoregions of the Conterminous United States. Annals of the Association of
American Geographers 77:118-125.
Postel, S. and S. Carpenter 1997. Freshwater Ecosystem Services. Nature's Services: Societal
Dependence on Natural Ecosystems. G. C. Daily. Washington, D.C., Island Press: 195-214.
Schriver, P. J. Bogestrand, E. Jeppesen, M. Sondergaard.. 1995. Impact of submerged
macrophytes on fish-zooplankton-phytoplankton interactions: Large scale enclosure experiments in
a shallow eutrophic lake. Freshwater Biology 33: 255-270.
Stahl, L.L., B.D. Snyder, A.R. Olsen, J.L. Pitt. 2009. Contaminants in Fish Tissue from US Lakes
and Reservoirs: a National Probabilistic Study. Environ. Monitoring Assess. 150:3-19.
Stein, E. and B. Bernstein, 2008. Integrating Probabilistic and Targeted Compliance Monitoring for
Comprehensive Watershed Assessment. Environ. Monitoring assess. 144:117-129.
Stoddard, J.L., D. Jefferies, A. Lukewille, T. Clair, P. Dillion, C. Driscoll, M. Forsius, M. Johannessen,
J. Kahl, J Kellogg, A. Kemp, J. Mannio, D. Monteith, P. Murdoch, S. Patrick, A. Rebsdorf, B. Skelvale,
M. Stainton, T. Traden, H. VanDam, K. Webster, J. Dieting and A. Wilander. 1999. Regional Trends
in Aquatic Recovery from Acidification in North America and Europe. Nature 401:575-578.
Taillon, D. and M. G. Fox. 2004. The Influence of Residential and Cottage Development on Littoral
Zone Fish Communities in a Mesotrophic Ontario Lake. Environ. Biol. Fishes 71: 275-285.
U.S. EPA. 1974. National Eutrophication Survey Methods for Lakes Sampled in 1972. Working
Paper No. 1. EPA Office of Research and Development, Washington, DC 20460, pp. 40.
U.S. EPA. 1975a. National Eutrophication Survey Methods 1973 - 1976. Working Paper No. 175.
EPA Office of Research and Development, Washington, DC 20460, pp.90.
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
-------
Chapter 9 Next Steps for the National Surveys
U.S. EPA. 1975b. National Eutrophication Survey Data Acquisition and Laboratory Analysis System
for Lake Samples. EPA-600/4-75-015. EPA Environmental Monitoring and Support Laboratory, Las
Vegas, NV 89114, pp 21.
U.S. EPA. 2000. A Benefits Assessment of Water Pollution Control Programs Since 1972: Part 1.
The Benefits of Point Source Controls for Conventional Pollutants in Rivers and Streams, http://
yosemite.epa.gov/ee/epa/eerm.nsf/vwAN/EE-0429-01.pdf/$file/EE-0429-01.pdf
U.S. EPA. 2000. Nutrient Criteria Technical Guidance Document - Lakes. Washington, DC. EPA-
822-BOO-001.
U.S. EPA. 2003. Stoddard, J.L., J.S. Kahl, F.A. Deviney, D.R. DeWalle, C.T. Driscoll, A.T. Herlihy, J.H.
Kellogg, P.S. Murdoch, J.R. Webb, and K.E. Webster. Response of Surface Water Chemistry to the
Clean Air Act Amendments of 1990. EPA/620/R-03/001. Research Triangle Park, NC.
U.S. EPA. 2008. Report on the Environment, http://www.epa.gov/ncea/roe.
U.S. General Accounting Office. 2000. Water Quality - Key EPA and State Decisions Limited
by Inconsistent and Incomplete Data. GAO/RCED-00-54. Governmental Accountability Office,
Washington, D.C.
Van Sickle, J. and S.G. Paulsen. 2008. Assessing the Attributable Risks, Relative Risks, and
Regional Extents of Aquatic Stressors. J. N.Amer Benthol. Soc. 27:920-931.
Wade, T.J., R. Calderon, E. Sams, M. Beach, K. Brenner, A. Williams, and Dufour. 2006. Rapidly
Measured Indicators of Recreational Water Quality are Predictive of Swimming-Associated
Gastrointestinal Illness. Environmental Health Perspectives 114: 24-28.
Wagner, T. A. Jabar, M. Bremigan. 2006. Can Habitat Alteration and Spring Angling Explain
Largemouth Bass Nest Success? Transactions of the American Fisheries Society 135:843-852.
Wilson, M. and S. Carpenter 1999. Economic Valuation of Freshwater Ecosystem Services in the
United States: 1971-1997. Ecological Applications 9(3): 772-783.
Whittier, T, S. Paulsen, D. Larsen, S. Peterson, A. Herlihy, P. Kaufmann. 2002. Indicators of
Ecological Stress and their Extent in the Population of Northeastern Lakes: A Regional Scale
Assessment. Bioscience 52:3, 235-247.
U.S. EPA. 2009. The National Study of Chemical Residue in Lake Fish Tissue, http://www.epa.gov/
waterscience/fish/study/data/finalreport.pdf
National Lakes Assessment: A Collaborative Survey of the Nation's Lakes
------- |